Brominated polystyrenic resins

[0002] This application is a continuation-in-part of commonly-owned application Ser. Nos. 09/151,193, filed Sep. 10, 1998, 09/151,194, filed Sep. 10, 1998, and 09/170,487, filed Oct. 13, 1998, now U.S. Pat. Nos. 6,232,408, 6,232,393 and 6,235,844 respectively. Each of said application Ser. Nos. 09/151,193, 09/151,194, and 09/170,487, are continuations-in-part-of commonly-owned application Ser. No. 08/852,462, filed May 7, 1997 now abandoned and of commonly-owned application Ser. No. 08/872,985, filed Jun. 11, 1997, now U.S. Pat. No. 5,852,132. Said application Ser. No. 09/151,194 is a continuation-in-part of commonly-owned application No. 09/041,632, filed Mar. 13, 1998, now U.S. Pat. No. 5,916,978, which is a continuation of commonly-owned application Ser. No. 08/846,156, filed Apr. 25, 1997, now U.S. Pat. No. 5,767,203, which in turn is a continuation of commonly-owned application No. 08/721,389, filed Sep. 26, 1996, now abandoned, and said application No. 08/872,985 is in turn a continuation of said commonly-owned application Ser. No. 08/727,341, filed Sept. 26, 1996, now U.S. Pat. No. 5,677,390.

[0003] Other commonly-owned copending applications or commonly-owned patents relating to subject matter in this general field are application Nos. 09/151,110, filed Sep. 10, 1998, 09/153,502, filed Sep. 15, 1998, and 09/291,428, filed Apr. 13, 1999, and U.S. Pat. Nos. 5,686,538; 5,852,131; and 6,133,381.

[0004] This invention relates to novel, improved high quality brominated styrenic polymers eminently well suited for use as flame retardants in thermoplastic polymer compositions.

[0005] Brominated polystyrenes are well established as flame retardants for use in thermoplastics, e.g., polybutylene terephthalate, polyethylene terephthalate and nylon (a.k.a. polyamides). Recently, interest has been shown for expanding their use to syndiotactic polystyrene and polycyclohexylene dimethylene terephthalate. Generally, brominated polystyrenes are produced by a reaction between polystyrene and a brominating agent (e.g., bromine or bromine chloride) in the presence of a solvent (e.g., dichloroethane) and a Lewis acid catalyst. Heretofore the art has proffered many processes which are claimed to produce a superior brominated polystyrene. See, for example, U.S. Pat. Nos. 4,200,703; 4,352,909; 4,975,496 and 5,532,322.

[0006] Despite these efforts, previously-known brominated polystyrene flame retardants remain deficient in certain properties which translate into deficient performance of thermoplastic polymer blends in which they are used when the blends are subjected to polymer processing conditions.

[0007] To better understand some of the reasons for these deficiencies, it is helpful to consider some of the structural characteristics of previously known brominated polystyrenes. To begin with, the bromine content of a brominated polystyrene is the sum of (1) the bromine which is substituted onto the aromatic portions of the polymer, (2) the bromine which is substituted onto the aliphatic portion(s) of the polymer, e.g., the polymer backbone or alkyl substitution which is present due to alkylation of the aromatic portion of the polymer, and (3) any ionic bromine present, e.g., sodium bromide. The alkylation of aromatic rings in the brominated polystyrene is catalyzed by the Lewis acid catalyst used in producing the brominated styrenic polymer, and the reaction solvent (usually a 1-3 carbon atom dihaloalkane) serves as the alkylating agent. The bromine for (1) is referred to herein as aromatic bromide, while the bromine for (2) is referred to as aliphatic bromide. Even though ionic bromine can contribute to the total bromine content, its contribution to the total bromine content is small. Nevertheless, as pointed out in U.S. Pat. No. 5,328,983, ionic impurities in brominated polystyrene may degrade polymer formulations in respect to their ultimate electrical properties, and also may result in corrosion of processing equipment or in the corrosion of metallic parts in their end-use applications.

[0008] Aliphatic halide content of brominated polystyrenes is not desirable as aliphatic halide is not as thermally stable as aromatic halide and, thus, aliphatic halide can be easily converted to hydrogen halide, e.g., HBr or HCl, under normal end-use processing conditions. Aliphatic bromide and chloride are generally referred to by the art and quantified, respectively, as hydrolyzable bromide and hydrolyzable chloride since such halides are easily hydrolyzed as compared to aromatic halides.

[0009] Corrosion of metal processing equipment such as melt blenders, extruders, and molding machines, attributable to the release of hydrogen halide from prior brominated polystyrene flame retardants when molding thermoplastic polymers containing such flame retardants under thermal processing conditions is thus one deficiency of such flame retardants. In the presence of moisture, hydrogen chloride and hydrogen bromide released from the brominated polystyrene in the blend during exposure to the elevated polymer processing temperatures can result in acid formation and consequent metal corrosion.

[0010] To evaluate brominated styrenic polymers for their tendencies to release hydrogen halide under thermal processing conditions, use is made of the method described in U.S. Pat. No. 5,726,252 and referred to therein as the Thermal Stability Test Procedure. In essence, this method indicates the content of halogen atoms in the brominated polystyrene that is not bonded directly to the aromatic rings and thus is more readily released from the polymer when at elevated temperature. The Thermal Stability Test is described in greater detail hereinafter.

[0011] Prior brominated polystyrenes have oftentimes been deficient in their color characteristics. The manufacturer of molded thermoplastic articles generally finds it of advantage to have available a flame retardant which will not contribute excessive color to the molded products or otherwise interfere with color matching specifications applicable to a given product. Thus in general, the lower the color of the brominated styrenic polymer (i.e., the whiter the flame retardant), the better.

[0012] For many applications it is desirable to have a flame retardant which produces polymer blends having good flow characteristics. Good flow characteristics can significantly reduce processing time in the manufacture of molded thermoplastic products. In addition, good molten polymer flow tends to ensure that the molds are completely filled, thereby resulting in products with better surface characteristics and appearance.

[0013] The chlorine content of brominated polystyrenes is credited to chlorine which, like the bromine, is chiefly part of the polymer structure as an aromatic and/or an alkyl chloride. The use of bromine chloride as the brominating agent is the largest contributor to the chlorine content. However, chlorinated solvents and/or chlorine-containing catalysts used in the production of the brominated polystyrene may also contribute to the chlorine content of the brominated polystyrene. Apart from whether the halide is present as an aromatic or aliphatic halide, it is also desirable to minimize the total chlorine content of the brominated polystyrene as chlorine is not as efficacious or as stable a flame retardant constituent as is bromine.

[0014] Prior art brominated polystyrene polymers that have been evaluated for thermal stability have exhibited a 1% weight loss at temperatures less than 336° C. when submitted to Thermogravimetric Analysis (TGA) and, indeed, most have exhibited a 1% weight loss at temperatures around 300° C. Such low TGA 1% weight loss thermal stability temperatures, while acceptable in actual practice, are much less desirable than TGA 1% weight loss thermal stability temperatures of 340° C. or above, especially under the high temperatures to which flame retarded thermoplastics formulated with such brominated polystyrene polymers are exposed during processing.

[0015] It would be especially desirable if most if not all of the above-mentioned disadvantages of brominated polystyrenes could be avoided or at least minimized. For example, it would be of considerable advantage if a more thermally stable brominated styrenic polymer, e.g., brominated polystyrene, could be provided that releases minimal amounts of hydrogen halide under thermal processing conditions, thereby greatly reducing the opportunity for corrosion of processing equipment to occur. It would be especially desirable and of considerable advantage, if a brominated styrenic polymer, e.g., brominated polystyrene, could be provided that has both improved melt flow characteristics and improved thermal stability. It would also be of great advantage if these improvements could be achieved without material sacrifice of other important properties, and if possible with concomitant provision of other desirable properties such as low ionic bromide content, minimal (if any) chlorine content, and/or less odor properties due to solvent residues. It would also be very desirable and advantageous if, in addition to high thermal stability in the Thermal Stability test, a brominated styrenic polymer, e.g., brominated polystyrene, could exhibit low color-forming tendencies, and improved melt flow properties. It would also be of considerable advantage if a brominated styrenic polymer, e.g., brominated polystyrene, could be provided that, even though it has a total bromine content of 60 wt % or more, and indeed of 67 wt % or more, possesses the combination of improved melt flow properties and low color-forming tendencies plus one or more other desirable properties. It would be of even further advantage if each or all of the foregoing advantages could be achieved with brominated styrenic polymers, e.g., brominated polystyrenes, that have very low chlorine contents. Also, it would be highly advantageous if a brominated styrenic polymer, e.g., brominated polystyrene, could be provided that possesses the combination of a total bromine content of 50 wt % or 60 wt % or more, improved melt flow properties, low color-forming tendencies, and a TGA temperature for a 1% weight loss, when submitted to thermogravimetric analysis under nitrogen, of 340° C. or above. And it would be even more advantageous if, in addition, this combination could be achieved with a brominated styrenic polymer, e.g., brominated polystyrene, that has a thermal stability in the Thermal Stability test of 200 ppm or less, preferably 150 ppm or less, and especially 100 ppm or less.

[0016] This invention is deemed to enable the achievement of most, if not all, of the above-mentioned advantages in a highly satisfactory manner.

[0017] In accordance with one embodiment of this invention, new, high quality brominated styrenic polymers are provided that release minimal amounts of hydrogen halide under thermal processing conditions, thereby greatly reducing the opportunity for corrosion of processing equipment to occur during polymer processing operations. In addition, these new brominated styrenic polymers possess or exhibit other superior properties or characteristics enhancing their utility as flame retardants for thermoplastic polymers of various types, including for example high-impact polystyrenes, glass-filled polyesters and glass-filled nylons.

[0018] Thus one embodiment of this invention is a brominated styrenic polymer having (i) a total bromine content above about 50 wt % (preferably above about 60 wt %, and more preferably at least about 67 wt %), and (ii) thermal stability in the Thermal Stability Test described hereinafter of 200 ppm HBr or less, preferably 150 ppm of HBr or less, and more preferably 100 ppm of HBr or less. Such brominated styrenic polymer is especially suitable for use as a flame retardant when blended in at least a flame retardant amount with a thermoplastic polymer, preferably a thermoplastic engineering thermoplastic polymer. Particularly preferred in this embodiment is a brominated styrenic polymer which is further characterized in that it has, prior to blending, a chlorine content, if any, of less than about 700 ppm Cl (more preferably, less than about 500 ppm Cl, and still more preferably less than about 100 ppm Cl).

[0019] Another embodiment is a brominated styrenic polymer having (i) a total bromine content above about 50 wt % (preferably above about 60 wt %, and more preferably at least about 67 wt%), (ii) a TGA temperature for 1% weight loss which is 340° C. or higher, preferably within the range of from about 340° C. to about 380° C., and more preferably within the range of from about 345° C. to about 380° C., and (iii) thermal stability in the Thermal Stability Test described hereinafter of 200 ppm HBr or less, preferably 150 ppm of HBr or less, and more preferably 100 ppm of HBr or less. Such brominated styrenic polymer is especially suitable for use as a flame retardant when blended in at least a flame retardant amount with a thermoplastic polymer, preferably a thermoplastic engineering thermoplastic polymer. Particularly preferred in this embodiment is a brominated styrenic polymer which is further characterized in that it has a chlorine content, if any, of less than about 700 ppm Cl (more preferably, less than about 500, and still more preferably less than about 100 ppm Cl).

[0020] The above brominated styrenic polymers of this invention are preferably a brominated polystyrene.

[0021] Pursuant to a preferred embodiment of this invention there is provided a brominated anionic styrenic polymer, preferably a brominated anionic polystyrene, that has (i) a total bromine content above about 50 wt %, preferably at least about 60 wt %, more preferably at least about 67 wt %, and still more preferably at least about 68 wt%; (ii) a thermal stability in the Thermal Stability Test of 200 ppm of HBr or less, preferably 150 ppm of HBr or less, and more preferably 100 ppm of HBr or less; and (iii) a ΔE color value, measured using 10 wt % solutions in chlorobenzene, of less than about 10, preferably less than about 7. and more preferably less than about 5. More preferred brominated anionic styrenic polymers of this embodiment such as brominated anionic polystyrenes have GPC weight average molecular weights in the range of about 5000 to about 30,000, preferably in the range of about 7000 to about 25,000, and more preferably in the range of about 8000 to about 20,000.

[0022] Another preferred embodiment of this invention is a brominated anionic styrenic polymer, preferably a brominated anionic polystyrene, that has (i) a total bromine content above about 50 wt %, preferably at least about 60 wt %, more preferably at least about 67 wt %, and still more preferably at least about 68 wt %; (ii) a thermal stability in the Thermal Stability Test of 200 ppm HBr or less, preferably 150 ppm of HBr or less, and more preferably 100 ppm HBr or less; and (iii) a melt flow index of at least about 20 g/10min, preferably at least about 25 g/10 min, and more preferably at least about 30 g/10 min in the Melt Flow Index Test as described hereinafter. More preferred brominated anionic styrenic polymers of this embodiment such as brominated anionic polystyrenes have a GPC weight average molecular weight in the range of about 5000 to about 30,000, preferably in the range of about 7000 to about 25,000, and more preferably in the range of about 8000 to about 20,000.

[0023] Still another preferred embodiment of this invention is a brominated anionic styrenic polymer, preferably a brominated anionic polystyrene, that has (i) a total bromine content above about 50 wt %, preferably at least about 60 wt %, more preferably at least about 67 wt %, and still more preferably at least about 68 wt %; and (ii) a melt flow index of at least about 20 g/10 min, preferably at least about 25 g/10 min, and more preferably at least about 30g/10 min in the Melt Flow Index Test as described hereinafter. In more preferred embodiments, these brominated styrenic polymers such as brominated polystyrene also have (I) a ΔE color value, measured using 10 wt % solutions in chlorobenzene, of less than about 10, preferably less than about 7, and more preferably less than about 5; or (II) a TGA temperature for a 1% weight loss under nitrogen of at least about 340° C., and preferably at least about 350° C.; or (III) a GPC weight average molecular weight in the range of about 5000 to about 30,000, preferably in the range of about 7000 to about 25,000, and more preferably in the range of about 8000 to about 20,000. Still more preferred compositions of this embodiment possess at least any two of (I), (II), and (III), e.g., (I) and (II); (I) and (III); or (II) and (III). Even more preferred are compositions of this embodiment that possess all three of (I), (II), and (III).

[0024] A further preferred embodiment of this invention is a brominated anionic styrenic polymer, preferably a brominated anionic polystyrene, that has (i) a total bromine content above about 50 wt %, preferably at least about 60 wt %, more preferably at least about 67 wt %, and still more preferably at least about 68 wt %; (ii) a ΔE color value, measured using 10 wt% solutions in chlorobenzene, of less than about 10, preferably less than about 7, and more preferably less than about 5; and (iii) a GPC weight average molecular weight in the range of about 5000 to about 30,000, preferably in the range of about 7000 to about 25,000, and more preferably in the range of about 8000 to about 20,000. In more preferred embodiments, these brominated styrenic polymers such as brominated polystyrene also have a TGA temperature for a 1% weight loss under nitrogen of at least about 340° C., and preferably at least about 350° C.

[0025] Still another preferred embodiment of this invention is a brominated anionic styrenic polymer, preferably a brominated anionic polystyrene, that has (i) a total bromine content above about 50 wt %, preferably at least about 60 wt %, more preferably at least about 67 wt %, and still more preferably at least about 68 wt %; (ii) a thermal stability in the Thermal Stability Test of 200 ppm HBr or less, preferably 150 ppm of HBr or less, and more preferably 100 ppm HBr or less; (iii) a melt flow index of at least about 20 g/10 min, preferably at least about 25 g/10 min, and more preferably at least about 30 g/10 min in the Melt Flow Index Test as described hereinafter; and (iv) a ΔE color value, measured using 10 wt % solutions in chlorobenzene, of less than about 10, preferably less than about 7, and more preferably less than about 5. In more preferred embodiments, the brominated styrenic polymers such as brominated polystyrene described in this paragraph are further characterized in that they have a GPC weight average molecular weight in the range of about 5000 to about 30,000, preferably in the range of about 7000 to about 25,000, and more preferably in the range of about 8000 to about 20,000; and/or a TGA temperature for a 1% weight loss under nitrogen of at least about 340° C., and preferably at least about 350° C.

[0026] A further preferred embodiment of this invention is a brominated anionic styrenic polymer, preferably a brominated anionic polystyrene, that has (i) a total bromine content above about 50 wt %, preferably at least about 60 wt %, more preferably at least about 67 wt %, and still more preferably at least about 68 wt %; (ii) a thermal stability in the Thermal Stability Test of 200 ppm HBr or less, preferably 150 ppm HBr or less, and more preferably 100 ppm HBr or less; and (I) that is essentially free of impurities selected from the group consisting of (a) methylene chloride, (b) ethylene dichloride, and especially (c) bromodichloroethane, (d) dibromochloroethane, (e) dibromodichloroethane, (f) tribromochloroethane, and (g) any mixture of two or more of the foregoing, especially a mixture that contains at least one of (c) through (f); (II) that has an ionic bromine content of 2000 ppm or less, preferably 1500 ppm or less, more preferably 1000 ppm or less, and still more preferably 500 ppm or less; or (III) that contains, if any, less than about 700 ppm Cl, preferably less than 500 ppm Cl, and more preferably less than 100 ppm Cl. More preferred compositions of this embodiment possess at least any two of (I), (II), and (III), e.g., (I) and (II); (I) and (III); or (II) and (III). Still more preferred are compositions of this embodiment that possess all three of (I), (II), and (III).

[0027] In prior commonly-owned copending application Ser. Nos. 09/151,193; 09/151,194; and 09/170,487, it is indicated to be preferable, or even desirable because of cost and lack of ready availability, not to employ anionically-produced polystyrene in forming brominated polystyrenes. Nevertheless brominated polystyrenes made from anionic polystyrenes pursuant to this invention possess a combination of excellent properties. Such properties include, for example, very high thermal stability in the Thermal Stability test, very low ΔE color value, and high melt flow even with bromine contents of 67 wt % or more. Moreover, tests conducted using brominated polystyrenes produced from anionic polystyrenes by other entities known for their expertise in the field of brominated polystyrenes showed that those products were substantially inferior in properties.

[0028] Other embodiments and features of this invention will be further apparent from the ensuing description and appended claims.

[0029] FIG. 1 is a schematic diagram depicting a process suitable for producing preferred brominated polystyrenes of this invention.

[0030] All ppm levels referred to in this document are on a weight basis, and are based on the total weight of the brominated styrenic polymer.

[0031] Brominated Styrenic Polymers

[0032] As noted above, the brominated styrenic polymers of this invention are brominated styrenic polymers, (preferably a brominated polystyrene). These brominated styrenic polymers have a total bromine content of at least about 50 wt %, preferably above about 60 wt %, and more preferably at least about 67 wt %. All wt % and ppm levels herein being based on the total weight of the brominated styrenic polymer, unless otherwise stated. Moreover, the brominated styrenic polymers (preferably brominated polystyrenes) of this invention possess certain additional important properties or characteristics in accordance with the above Summary of the Invention. These properties or characteristics pertain to such factors as thermal stability in the Thermal Stability Test described hereinafter, very low ΔE color values measured using 10 wt % solutions in chlorobenzene as described hereinafter, desirable melt flow indices as measured using the Melt Flow Index Test described hereinafter, desirable GPC weight average molecular weights using procedures described hereinafter, total chlorine content (if any), and freedom from specified impurity contents. Other properties of brominated styrenic polymers of this invention will be apparent as the description proceeds.

[0033] This invention can provide a novel thermally stable brominated polystyrene which is comprised of polymer units having the formula:

[0034] wherein each X is independently —H or a halide atom, the identity of each X for each polymer unit being such that the brominated polystyrene contains less than about 6000 ppm of X-type halide atoms, and wherein the value of n for each polymer unit is such that the brominated polystyrene contains at least 50 wt % bromine. From an economic and performance standpoint, it is preferred that the bromine content be within the range of from above 60 wt % to about 70-71 wt % (n=about 1.9 to about 2.9-3.0), and especially within the range of from about 68 wt % to about 71 wt % (n=about 2.7 to about 3.0).

[0035] With regard to the halide atoms, X, preferred brominated polystyrenes will be those in which X is bromide. Such polymers may contain some chlorine atoms, but the amount will be insignificant, usually less than about 500 ppm, and where possible, less than about 100 ppm. If chlorine is present, its source would probably be the Lewis acid catalyst or the solvent used in the preparation of the brominated polystyrene. Preferred brominated polystyrene polymers are those in which the chlorine content is less than 500 ppm in accordance with X-Ray Fluorescence analysis. It is beneficial, from the viewpoint of economy and performance, that the X-type bromide content be less than about 4000 ppm, say within the range of from about 1000 ppm to about 3000 ppm. Most beneficial are those X-type bromide contents which are within the range of from 0 ppm to about 1500 ppm.

[0036] The brominated polystyrenes of this invention are unique in that, from their very inception, the polymer has the very low X-type halide content discussed above. This is an important aspect as the polymers do not need further treatment to reduce the X-type halide content. Reduction of the X-type halide content, say by hydrolysis, is not desirable as it yields a polymer having hydroxyl, ether, and/or olefinic functionality in its structure which can alter polymer properties. It is preferred that the brominated polystyrenes of this invention contain little or no hydrolysis residues, say less than about 500 ppm and preferably less than about 100 ppm.

[0037] As noted above, one of the striking features of this invention is the ability of providing brominated styrenic polymers such as brominated polystyrenes having exceptional stability in the Thermal Stability test. This means that in preferred brominated styrenic polymers of this invention, the amount of HBr released under the stringent test conditions is very small, 200 ppm or less, and in many cases less than 100 ppm. This in turn minimizes, if not eliminates, corrosion of thermoplastic polymer processing equipment when processing a thermoplastic polymer containing a flame retardant quantity of a preferred brominated styrenic polymer of this invention at elevated polymer processing temperatures.

[0038] Preferred brominated styrenic polymers of this invention will be those which provide, at the lowest cost, the highest bromine content and the lowest X-type halide content which obtain the desired properties referred to above. Other preferred embodiments of this invention are brominated anionic styrenic polymers produced as described hereinafter and which can provide unprecedented superior properties and combinations of superior properties.

[0039] Preferred brominated styrenic polymers of this invention exhibit a combination of superior physical properties, e.g., little or no color or odor resulting from solvent residues. For flame retardants, color is an important property, with pure white being the ultimate goal. Due to the formation of various color bodies by all bromination processes, the industry has accepted near-white products as being acceptable. The color of prior art brominated polystyrene, expressed as a solution ΔE value, generally will fall within the range of 20 to 35. In distinction, brominated polystyrenes of this invention typically feature ΔE values (10 wt % in chlorobenzene) of less than 20, e.g., within the range of from about 2 to about 15, and preferably within the range of from about 2 to about 18. In fact, it has been found possible to produce pursuant to this invention brominated polystyrenes having ΔE values (10 wt % in chlorobenzene) of 10 or less. Indeed, as will be shown hereinafter, a plurality of brominated polystyrenes of this invention formed as described hereinafter using anionic polystyrenes had ΔE values (10 wt % in chlorobenzene) of 7 or less, and in most cases ΔE values of less than 5. Moreover, all of these particular brominated polystyrenes of this invention had thermal stabilities in the Thermal Stability test of less than 100 ppm HBr.

[0040] Another physical property of preferred brominated styrenic polymers of this invention is that they have essentially no odor, or very little odor, attributable to solvent residues, when heated to a temperature above 150° C. In comparison, Pyro-Chek® 68PB brominated polystyrene flame retardant (Ferro Corporation) has a noticeable and strong odor at 1 50° C. The strong odor is believed to be attributable to the presence of bromochloroethanes, e.g., bromodichloroethane, dibromochloroethane, dibromodichloroethane and tribromochloroethane, which are in the Pyro-Chek® 68PB product. Such bromochloroethanes are not seen in detectable quantities in the brominated styrenic polymers of this invention.

[0041] Styrenic Polymer Reactants

[0042] Styrenic polymers which are brominated to form the brominated styrenic polymers of this invention are homopolymers and copolymers of vinyl aromatic monomers. Preferred vinyl aromatic monomers have the formula:

[0043] H₂C═CR—Ar

[0044] wherein R is a hydrogen atom or an alkyl group having from 1 to 4 carbon atoms and Ar is an aromatic group (including alkyl-ring substituted aromatic groups) of from 6 to 10 carbon atoms. Examples of such monomers are styrene, alpha-methylstyrene, ortho-methylstyrene, meta-methylstyrene, para-methylstyrene, para-ethylstyrene, isopropenyltoluene, vinylnaphthalene, isopropenylnaphthalene, vinylbiphenyl, vinylanthracene, the dimethylstyrenes, tert-butylstyrene, the several bromostyrenes (such as the monobromo-, dibromo-, and tribromo-variants). Polystyrene is the preferred reactant. When the brominated styrenic polymer is made by bromination of a copolymer of two or more vinyl aromatic monomers, it is preferred that styrene be one of the monomers and that styrene comprise at least 50 weight percent of the copolymerizable vinyl aromatic monomers. If a bromo styrenic polymer is selected for bromination to make a brominated styrenic polymer, the initial bromostyrenic polymer must have a lower bromine content than the bromine content to be present in the brominated styrenic polymer of this invention. In this connection, the terms “brominated styrenic polymer” and “brominated polystyrene” as used in the specification and in the claims hereof refer to a brominated polymer produced by bromination of a pre-existing styrenic polymer such as polystyrene or a copolymer of styrene and at least one other vinyl aromatic monomer, as distinguished from an oligomer or polymer produced by oligomerization or polymerization of one or more brominated styrenic monomers, the properties of the latter oligomers or polymers being considerably different from brominated polystyrene in a number of respects.

[0045] The styrenic polymer reactant used in the production of the brominated styrenic polymers of this invention can be produced by free-radical polymerization, cationically-initiated polymerization, or anionically-initiated polymerization, with the latter being preferred for achieving the combination of the high melt flows together with high thermal stabilities in the Thermal Stability Test and/or the very low ΔE color values referred to above. In fact, surprisingly, when produced as described hereinafter, brominated polystyrenes of this invention made from anionic polystyrenes exhibited a combination of desirable properties that far exceeded the properties exhibited by samples of brominated anionic polystyrenes prepared by and received from other industrial concerns known for their prowess in the field of brominated polystyrenes made by bromination of polystyrenes. Thus while EPO 0 201 411 refers to use of anionic polystyrene in forming brominated polystyrene for achieving reduced color, other properties of those brominated polymers are considerably inferior to the properties achieved when using anionic polystyrenes pursuant to this invention.

[0046] The aromatic pendant constituents of the polymer can be alkyl substituted, but in most cases, will not be so substituted. The polystyrene used to produce the brominated polystyrenes of this invention will have a M_wwithin the range of from about 500 to about 500,000 and a polydispersity within the range of from above about 1 to about 4. For most general purposes, the polystyrene reactant will have a M_wwithin the range of from about 100,000 to about 300,000 and will have a polydispersity within the range of from about 1.25 to about 2.5. The lower molecular weight polystyrene reactants will have a M_wwithin the range of from about 500 to about 100,000 and a polydispersity less than about 10 and preferably within the range of from above 1 to about 4. Preferred are anionic styrenic polymers, and where high melt flow indices are desired, it is desirable to conduct the bromination as described hereinafter using anionic styrenic polymers such as anionic polystyrene having GPC weight average molecular weights in the range of about 500 to about 15,000, preferably in the range of about 1000 to about 10,000, and more preferably in the range of about 2000 to about 8000. Higher molecular weight polymer reactants of this invention have a M_wwithin the range of from about 300,000 to about 500,000 and a polydispersity within the range of from above 1 to about 4. The M_wand polydispersity values are both based on gel permeation chromatography (GPC) techniques which are hereinafter described.

[0047] It has also been found preferable that the polystyrene used in the formation of the brominated polystyrenes flame retardant not contain any additives, such as zinc stearate, paraffins, mineral oils and the like. In cases where high melt flow is not required, one highly preferred polystyrene is Styron® 612 which is marketed by The Dow Chemical Company. However, additive-containing polystyrene such as Styron 668, Styron 677, Styron 680 of The Dow Chemical Company, as well as EA 3300, MB 3200, MC 3100, or EA 3000 of Chevron Chemical Company, or equivalent materials from other producers, can be used. Relatively low molecular weight polystyrenes formed by cationically-initiated polymerization such as Piccolastic A5, Piccolastic A75, or Piccolastic D125 of Hercules Incorporated can also be used. As noted above, in preferred embodiments of this invention where the combination of high melt flow and high thermal stability in the Thermal Stability Test and/or very low ΔE color values are required, anionic styrenic polymers, especially those with GPC weight average molecular weights of about 15,000 or below are preferred. Methods for producing anionic styrenic polymers are known and reported in the literature. See for example U.S. Pat. Nos. 4,442,273; 4,883,846; 5,717,040; and 5,902,865. Several preferred anionic polystyrenes are identified in Examples 23 through 33, infra.

[0048] Production of the Brominated Polystyrene

[0049] For purposes of simplification, much of the description hereinafter refers to preparation of brominated polystyrene, the preferred flame retardant of this invention. It will be appreciated that the principles and procedures described are applicable to preparation of other brominated styrenic polymers.

[0050] The brominated polystyrenes of this invention are not conventionally produced. Generally, a suitable process comprises feeding a mixture of bromine and a solution of bromochloromethane and polystyrene (2.5 to 5 moles of bromine per mole of polymerized styrene in the polystyrene) to a reactor containing a further amount of bromochloromethane and a catalytic amount of AlCl₃. The mixture of polystyrene, bromochloromethane and bromine is substantially free of a bromination catalyst. The phrase, “substantially free of a bromination catalyst”, is to be taken to mean less than a catalytically effective amount of catalyst. With such low amounts of catalyst, little or no catalyzed bromination or cross-linking should occur. Generally, such amounts will be less than 500 ppm based on the weight of polystyrene reactant present. The reaction temperature will be within the range of from about −10° C. to about 15° C. Preferably, the reaction is conducted at one or more temperatures in the range of about −10° C. to about 10° C. as this provides product of the highest quality and, surprisingly, the reaction itself proceeds at a suitably rapid rate at these low temperatures such that the process meets commercial production requirements. After the reaction mass is formed, it is usually maintained at reaction temperature for a period in the range of about 5 minutes to 2 hours, and preferably in the range of about 5 minutes to about 60 minutes. After this period, the reaction product is worked up by adding water and then settling to remove the acidic phase. Multiple water washes can be performed as desired. Next the reaction mass is treated with a base such as sodium hydroxide, sodium sulfite, and/or sodium borohydride, usually as an aqueous solution, to adjust the reaction pH to a suitable level of basicity and kill any remaining brominating agent. After these treatments, the reaction mass is settled to obtain a two-phase reaction mass containing an organic phase, which contains, as a solute, the brominated styrenic polymer product and an aqueous phase. The aqueous phase is decanted and the remaining organic phase is stripped of its solvent component. It is most convenient to accomplish this strip by pumping the organic phase into boiling water. As the solvent is flashed off, the brominated styrenic polymer product forms a precipitate. The precipitate can be recovered by any liquid-solid separation technique, e.g., filtration, centrifugation, etc. The recovered precipitate is then dried. If desired, especially in the case of free-radical polystyrenes, a thermal stabilizing amount of base can be incorporated in the finished brominated polystyrene composition. That is, the finished brominated polystyrene composition can be treated to contain an amount of alkali metal base such that if a sample of the finished composition is dissolved in bromochloromethane and the resultant solution is extracted with water, the aqueous extract has a pH of at least about 9.0, preferably a pH in the range of about 9.5 to about 11, and more preferably in the range of about 10 to about 10.5. Commonly-owned application Ser. No. 09/066,172, filed Apr. 24, 1998, describes processes in which a suitable amount of aqueous base is employed to improve the thermal stability of the resultant brominated polystyrene. A preferred way is to suitably increase the amount of base used during the catalyst deactivation stage so that a suitable residual amount of the base remains within the finished brominated polystyrene.

[0051] A preferred process can be used to ensure recovery of a purified brominated polystyrene polymer (or other brominated styrenic polymer) having a suitably low ionic halogen content (e.g., ionic bromine or ionic chlorine content) from the reaction mass formed by brominating polystyrene with bromine in a halocarbon or halohydrocarbon solvent having a boiling point below 100° C. and in the presence of a Lewis acid catalyst. Such preferred process comprises:

[0052] a) quenching the reaction mass in water to form an aqueous phase and an organic phase, and recovering the organic phase;

[0053] b) mixing the organic phase with water at a temperature in the range of about 10 to about 100° C. in a ratio of from about 0.02 to about 0.6 part by volume of the aqueous phase per each 1 part by volume of organic phase to form an aqueous extraction phase and an extracted organic phase, and recovering the extracted organic phase;

[0054] c) optionally but preferably, mixing inorganic alkali metal base and water with extracted organic phase from b) to form an alkaline mixture in which the pH of the aqueous phase in this mixture is in the range of about 7 to 14, and preferably in the range of about 10 to 14;

[0055] d) mixing a bromine scavenger and water with alkaline mixture from c) to form a bromine scavenged mixture;

[0056] e) precipitating brominated polystyrene by mixing bromine scavenged mixture from d) with a water solution of inorganic alkali metal base maintained at or above the boiling temperature of the halocarbon or halohydrocarbon solvent; and

[0057] f) recovering brominated polystyrene formed as a precipitate in e).

[0058] Before proceeding to step c) above, step b) above can be repeated one or more times as may be necessary or appropriate in achieving the desired reduction in ionic halogen (e.g., ionic bromine). Alternatively, step b) can be conducted on a continuous basis using liquid-liquid extraction apparatus such as a liquid-liquid extraction tower. Sodium sulfite and sodium borohydride are the preferred bromine scavengers for use in step d) above. However, other water-soluble inorganic sulfides such as lithium sulfite, potassium sulfite, magnesium sulfite, ammonium sulfite, etc., or other water soluble borohydrides such as lithium borohydride, potassium borohydride, etc., can be used. And in step d) above, a coalescing filter can be employed, if desired, to remove additional aqueous phase from the organic phase, and thereby still further reduce the ionic halogen content of the finished product.

[0059] In the production of brominated polystyrene, it is important that the iron content be kept to a minimum, say less than about 10 ppm iron. The introduction of iron into the product usually occurs due to iron equipment which is in contact with the reaction and product streams. Thus, it is preferred to use process equipment which does not act as a source of iron contamination. For example, the equipment can be glass-lined or corrosion resistant alloy.

[0060] A more detailed process description with reference to the accompanying drawing is given below.

[0061] Detailed Description of Bromination Process with Reference to the Drawing

[0062] Preferred process technology for producing brominated polystyrenes is described herein. It will be appreciated that, unless otherwise indicated in the specification hereof or specified in any claim hereof, this invention is not limited to use of all of this preferred process technology.

[0063] Polystyrenes useful for the production of the brominated polystyrenes by this preferred process are any of those which have been described above. Also, as mentioned previously, it is preferred that the polystyrene be additive-free.

[0064] The catalyst used in the preferred process can be any of the aluminum based catalysts, e.g., AlCl₃, AlBr₃and Al. Mixtures of aluminum catalysts can also be used. Once the catalyst has been added to the reaction system, it may undergo some reaction without significant loss of catalytic activity, e.g., AlCl₃may convert to some extent to AlBr₃. AlCl₃, because of its availability and price, is the catalyst of choice, and powder grade AlCl₃is most preferred due to its ease of dispersibility.

[0065] The catalyst is used in an amount which is sufficient to obtain the catalytic effect sought. These catalytic amounts will depend on the activity of the catalyst, but will generally fall within the range of from about 0.2 to about 10 weight percent and preferably within the range of from about 0.5 to about 5 weight percent, based on the weight of the styrenic polymer being brominated. The most active catalysts will be used in the lower amounts, while the less active catalysts will be used in the higher amounts. When AlCl₃is the catalyst, amounts within the range of from about 0.5 to about 3 weight percent are preferred.

[0066] The brominating agent is preferably bromine. Bromine can be obtained commercially in the diatomic form or can be generated by the oxidation of HBr. Br₂can be supplied either as a liquid or a gas. The amount of brominating agent used in the process should provide an overall mole ratio of total brominating agent to total styrenic polymer fed which will provide from about 1 to about 3 bromine substitutions per styrenic monomer unit in the polymer. It is preferred that the brominated polystyrene contain at least about 60 wt % bromine, more preferably at least about 67 wt % bromine, and desirably at least about 68 wt % bromine and most preferably within the range of from about 69 to 71 wt % bromine. For any particular styrenic polymer, the amount of brominating agent used in the process will be determined by the bromine content desired considering the highest bromine content which is obtainable with the process parameters chosen. The higher bromine contents will require the most brominating agent. It is pointed out that as perbromination is approached, it becomes more difficult to substitute the last bromines. Adding ever larger amounts of a brominating agent does not always attenuate this difficulty. The stoichiometry is easily determined as it requires one mole of Br₂per substitution sought. In practice, the practitioner will determine the bromine content sought on a weight basis and then will calculate, on an idealized basis, the number of moles of brominating agent needed to obtain the same. For example, if the styrenic polymer is polystyrene and the bromine content sought is 68 wt %, at least 2.7 moles of bromine per styrenic monomer unit will be required, not including any desired stoichiometric excess.

[0067] All of the bromine can be added with the polystyrene-bromochloromethane solution or a portion of the bromine can be pre-added to the reactor with the remainder being added with the solution. If pre-addition is to be used then the pre-added portion will amount to 0.5 to 20% of the total bromine used in the process.

[0068] While the foregoing describes the overall quantitative relationship between the brominating agent and styrenic polymer, the quantitative relationship between these two reactants in the feed mixture has not been fully discussed. Generally, the mixture which is to be fed is formed from about 1 to about 8 moles of brominating agent per mole of styrenic monomer units at any time during the feed period. During the feed, the quantitative relationship can be constant or can vary within the above-mentioned range. (It is possible to allow for some excursions outside of the range so long as such does not do significant harm to the process efficiency or to product quality.) A preferred range is from about 2.5 to about 5 moles of brominating agent per mole of styrenic monomer units to form the feed mixture. As can be appreciated, the use of an amount of brominating agent in the feed mixture which gives a mole ratio of brominating agent to styrenic monomer units which is less than or greater than the selected overall mole ratio of brominating agent to styrenic monomer units will result in exhaustion of either the brominating agent or the styrenic polymer as a mixture constituent before exhaustion of the other constituent. For example, if the practitioner chooses to produce brominated polystyrene with a 70 wt % bromine content, an overall molar ratio of bromine to styrenic monomer units of 3.0:1 would be suitable. If the practitioner chooses to form a feed mixture in which the molar ratio of bromine to styrenic monomer units is 1:1, it can be seen that the amount of polystyrene to be fed will be completed before obtaining the needed overall amount of bromine. In this case, the practitioner first uses the 1:1 mixture and then continues on with just a bromine feed after the polystyrene feed has been exhausted. If, on the other hand, the molar ratio in the feed mixture is chosen to be 5:1, then the bromine will first become exhausted and the feed will have to be finished with the polystyrene alone. Generally, it is preferred to have the overall molar ratio and the feed mixture ratio at least somewhat similar. In all cases though, the initial feed should preferably contain at least a molar ratio of bromine to styrenic monomer units of 1:1.

[0069] It is preferred that the bromine used in the process be essentially anhydrous, i.e., contain less than 100 ppm (weight basis) water and contain no more than 10 ppm organic impurities, e.g., oil, grease, carbonyl containing hydrocarbons, iron, and the like. Available, commercial grade bromine may have such purity. If, however, such is not available, the organic impurities and water content of the bromine can be conveniently reduced by mixing together a 3 to 1 volume ratio of bromine and concentrated (94-98 percent) sulfuric acid. A two-phase mix is formed which is stirred for 10-16 hours. After stirring and settling, the sulfuric acid phase, along with the impurities and water, is separated from the bromine phase. To further enhance the purity of the bromine, the recovered bromine phase can be subjected to distillation.

[0070] The preferred organic solvent for the bromination, namely, bromochloromethane, is preferably essentially anhydrous, containing less than 100 ppm (weight basis) water. It is most preferred that the solvent contain as little water as is practically obtainable, say between 0 to 30 ppm (weight basis).

[0071] The process benefits from the reaction mass being in an anhydrous condition. Water tends to affect the catalytic activity of the aluminum catalyst, which effect may hinder the quick aromatic bromination of the styrene rings. If, for some reason, the practitioner has large amounts of water in the process and dewatering is not practical, then it may be possible to overcome the situation by simply increasing the amount of catalyst used.

[0072] By forming a solution of bromochloromethane and styrenic polymer, the polymer becomes easy to handle and mix with bromine. These solutions preferably contain from about 5 to about 50 wt % polymer. More highly preferred are those which contain from about 5 to about 30 wt % polymer.

[0073] It is preferred to have the bromination catalyst, to which the bromine/styrenic polymer mixture is fed, to be in association with bromochloromethane so that the catalyst can be in a solution, slurry, dispersion or suspension. Such will enhance reaction mass mixing and mass transfer qualities. The mixture of bromochloromethane and catalyst is best described as a suspension. Generally, it is suitable to use from about 95 to about 99.9 wt %, preferably from about 99 to about 99.8 wt %, bromochloromethane, based on the total weight of bromochloromethane and catalyst.

[0074] The styrenic polymer/brominating agent mixture feed should occur expeditiously, with consideration being given to the ability of the process equipment to handle the heat load from the exothermic process, the evolving HBr, and other process concerns. In short, the feed can occur over the shortest time period that will be allowed by the equipment without excursion outside of critical process parameters. Generally, it is anticipated that the feed period will be from 0.5 to 3 hours for a commercial-size plant. Shorter feed periods are expected for smaller scale processes.

[0075] It is possible to conduct the bromination reaction at a temperature within the range of from about −20° C. to about 60° C. Desirably, the bromination temperature is maintained within the range of from about −10° C. to about 15° C. Most preferred temperatures are in the range of from about −10° C. to about 0°C. This last-mentioned temperature range provides product of the highest quality and, surprisingly, the reaction itself proceeds at a suitably rapid rate at these low temperatures such that the process meets commercial production requirements. The pressure can be atmospheric, subatmospheric or superatmospheric.

[0076] In carrying out the process, a bromination catalyst, preferably powdered AlCl₃, is suspended in essentially anhydrous bromochloromethane, to give an easily stirrable suspension. The suspension is prepared in a glass-lined, stirred reactor and brought to a temperature within the range of from about −10° C. to about −5° C. The mix is kept under an inert, dry atmosphere in the reactor. A solution of a styrenic polymer and bromochloromethane is prepared and intimately mixed with a bromine stream to yield a homogenous mixture. The mixture is fed into the stirred bromination catalyst suspension in the reactor. The intimate mixing of the styrenic polymer solution and bromine can be accomplished in a number of ways. For example, the solution and bromine can be fed to a mixing device, e.g., a mixing nozzle, at the lower end of the diptube in the reactor which extends to a point below the suspension level. The mixing device is designed to obtain the intimate mixing of the solution and bromine. Also, the mixing device acts to impart mixing energy, at the point of feed, to the intimate mixture and catalyst suspension. Another technique for obtaining intimate mixing of the styrenic polymer solution and brominating agent, is to use an exterior reactor loop having an in-line mixer, such as an impingement mixer. Generally, the use of an exterior reactor loop includes first charging the reactor with a bromination catalyst slurry, suspension, etc., and then withdrawing from the reactor a stream which is then fed to a mixer external of the reactor. A mixture formed from at least bromine and styrenic polymer is also fed to the mixer to yield a second mixture which is formed from the two feeds to the mixer. The second mixture is subsequently fed back to the reactor. The stream withdrawn from the reactor will initially comprise the catalyst. After the second mixture is fed to the reactor and the process runs, the withdrawn stream will begin to comprise brominated polystyrene along with catalyst.

[0077] Exemplifying the use of a reactor jet mixer, reference is made to FIG. 1 wherein there is shown a reactor, generally designated by the numeral 10. Reactor 10 is a stirred reactor, and initially it contains a suspension comprising catalyst and bromochloromethane. Reactor discharge conduit 40 provides a recycle stream from reactor 10 which is fed to pump 50. Pump 50 pressurizes the stream so that it is fed with force via conduit 70 back to reactor 10. Bromine is fed via conduit 20 to pump P₁while, at the same time, a solution of polystyrene and bromochloromethane is fed via conduit 22 to pump P_2.Pumps P₁and P₂feed jet mixer 24 via lines 26 and 28, respectively, to thereby produce an intimate mixture of bromine, polystyrene, and solvent. This intimate mixture is fed into the reaction mass in proximity to agitator 30 to ensure thorough mixing of the reactor contents. The removal of contents from, and their recycle back to, reactor 10, and also the feed of fresh reactants to jet mixer 24 are continued until at least substantially all of the bromine and polystyrene/bromochloromethane solution have been fed into the reaction mass.

[0078] As can be appreciated, the contents of reactor 10 change in composition during the bromine and bromochloromethane solution feeds. Initially, the contents of reactor 10 comprise catalyst and solvent. As the process runs, the reactor contents comprise and begin to become more rich in brominated polystyrene.

[0079] Irrespective of whether or not a diptube mixer or an exterior impingement mixer is used, the bromination of styrenic polymer will yield HBr as a major by-product. The HBr formed in the process first saturates the solvent and from then on HBr escapes into the head space above the reactor contents. It is preferred that the HBr be removed and passed to a water scrubber or stored as dry HBr. A dry, inert gas, e.g., nitrogen, can be used as a pad over the reactor contents to minimize the presence of water therein.

[0080] The reactor, in all cases, is preferably kept at a low temperature, e.g., from about −10° C. to about 10° C., during the feed of the styrenic polymer and/or brominating feed, as the case may be, and most preferably from about −10° C. to about 5° C. Also, after the feed is accomplished, the reactor is maintained at reaction temperature (desirably in the range of −10° C. to about 15° C. and preferably in the range of −10° C. to about 10° C.) for a period of from about 5 minutes to about 2 hours and preferably from about 5 to about 60 minutes. Such additional period of time following completion of the feed serves to continue the bromination until the desired degree of bromination has been achieved. Such period will be longer if the reaction parameters provide for mild bromination conditions during the bromine-polystyrene feed than if the parameters chosen provide for more severe bromination conditions during the feed. Also, such period will be longer if a high degree of bromination (e.g., above 69 wt % bromine in the brominated polystyrene) is sought. The reaction mass can be kept in the reactor during the additional period of time following completion of the feed. Also, the hold period can be used to strip more HBr from the reaction mass by using an inert gas sweep.

[0081] When the desired degree of bromination has been achieved, the preferred process described above for recovery of a purified brominated polystyrene polymer having a suitably low ionic halogen content involving steps a) through f) can be used. Another similar method for working up the reaction mass is to treat the reaction mass with water to deactivate the catalyst. Then the reaction mass is settled to remove the aqueous HBr phase. Sodium sulfite or sodium borohydride, typically as an aqueous solution, can then be added (and preferably is added) to remove any remaining brominating agent, followed by sodium hydroxide, again typically as an aqueous solution, to adjust the pH of the reaction mass. Although sodium sulfite and sodium borohydride are the preferred bromine scavengers for use in removing any remaining brominating agent, other water-soluble inorganic sulfides such as lithium sulfite, potassium sulfite, magnesium sulfite, ammonium sulfite, etc., or other water soluble borohydrides such as lithium borohydride, potassium borohydride, etc., can be used in as much as the scavenging function is performed by the sulfite or borohydride anion and/or by whatever other species may form when the inorganic sulfite or borohydride is dissolved in water. Aqueous solutions of the sulfite or borohydride can contain any suitable concentration of the dissolved inorganic sulfite or borohydride, and the amount of water-soluble sulfite or borohydride salt used should be at least sufficient to react with (destroy) the amount of residual brominating agent present in the mixture being treated. It is not necessary or advisable to use a large excess of sulfite or borohydride, e.g., more than about 2-3 mole % excess, as the excess represents wasted material serving no useful purpose. After scavenging the brominating agent, additional sodium hydroxide or other alkali metal base can be added, if desired, in a suitable amount and preferably in the form of an aqueous solution to act as a stabilizer for the brominated polystyrene. Whether or not such stabilizer is used, the reaction mass is settled to obtain a two-phase reaction mass containing an organic phase, which contains, as a solute, the brominated styrenic polymer product, and an aqueous phase. The aqueous phase is decanted and the remaining organic phase is stripped of its solvent component. It is most convenient to accomplish this strip by pumping the organic phase into boiling or near-boiling water. As the solvent is flashed off, particles of the brominated styrenic polymer product form in and separate from the residual liquid phase as a precipitate, and if desired, concurrently a suitable amount of the base can be incorporated into the particulate brominated polystyrene as it is being formed. If desired, a surfactant, such as dioctyl sulfosuccinate sodium salt, can be added to the hot water. The amount of dioctyl sulfosuccinate, if used, can be within the range of from about 0.01 to about 0.05 wt %, based upon the total weight of water and surfactant. The precipitate can be recovered by any liquid-solid separation technique, e.g., filtration, centrifugation, etc. The recovered precipitate is then dried.

[0082] Analytical Methods

[0083] Total Bromine Content. Since brominated styrenic polymers have good, or at least satisfactory, solubility in solvents such as tetrahydrofuran (THF), the determination of the total bromine content for the brominated styrenic polymers is easily accomplished by using conventional X-Ray Fluorescence techniques. The sample analyzed is a dilute sample, say 0.1±0.05 g brominated polystyrene in 60 mL THF. The XRF spectrometer can be a Phillips PW1480 Spectrometer. A standardized solution of bromobenzene in THF is used as the calibration standard. The total bromine values described herein and reported in the Examples are all based on the XRF analytical method.

[0084] Ionic Bromine Content. To determine the ionic bromine content of brominated styrenic polymers, the procedure used involves dissolving a sample of the polymer in a suitable organic solvent medium and titrating the solution with a standard solution of silver nitrate. In particular, a 2.0 gram sample of the brominated styrenic polymer weighed to the nearest 0.1 mg is placed in a 600 mL beaker, followed by 200 mL of tetrahydrofuran (THF), and a stir bar. The solids are stirred until completely dissolved. To this solution is added 50 mL of toluene, and the mixture is stirred. Immediately prior to conducting the titration, 50 mL of acetone, then 50 mL of isopropyl alcohol, and then 10 mL of glacial acetic acid are added to the sample mixture. The sample is then titrated immediately with standardized 0.01 N AgNO₃using an automatic potentiometric titrator such as a Metrohm670, 716, or 736, or equivalent. Reagent grade (A.C.S.) THF, toluene, acetone, isopropyl alcohol, and acetic acid are used in the procedure. The analysis is conducted using duplicate samples, plus a determination on a blank sample conducted in identical fashion except using no polymer. If both ionic bromine and ionic chlorine are present, the bromide titrates first. The distance between the inflection points is the chloride titre. The average of the two sample determinations is reported. However, if duplicate samples do not agree within less than 10% of each other, an additional replicate sample is analyzed in the same way, and the average of the three analyses is reported to three significant digits. The calculation for ionic bromine or chlorine are as follows: $\begin{array}{c}\mathrm{Ionic}\mathrm{bromine}\left(\mathrm{ppm}\right)=\frac{\mathrm{mL}{\mathrm{AgNO}}_3\times \mathrm{normality}\mathrm{of}{\mathrm{AgNO}}_3\times \left(7.99\right)\times {10}^4}{\mathrm{sample}\mathrm{weight}\mathrm{in}\mathrm{grams}}\\ \mathrm{Ionic}\mathrm{chlorine}\left(\mathrm{ppm}\right)=\frac{\mathrm{mL}{\mathrm{AgNO}}_3\times \mathrm{normality}\mathrm{of}{\mathrm{AgNO}}_3\times \left(3.545\right)\times {10}^4}{\mathrm{sample}\mathrm{weight}\mathrm{in}\mathrm{grams}}\end{array}$

[0085] mL AgNO₃=mL required for sample−mL required for blank

[0086] ΔE Color Value. To determine the color attributes of the brominated polymers of this invention, use is again made of the ability to dissolve brominated styrenic polymers in easy-to-obtain solvents, such as chlorobenzene. The analytical method used is quite straight-forward. Weigh 5 g ±0.1 g of the brominated polystyrene into a 50 mL centrifuge tube. To the tube also add 45 g ±0.1 g chlorobenzene. Close the tube and shake for 1 hour on a wrist action shaker. After the 1 hour shaking period, examine the solution for undissolved solids. If a haze is present, centrifuge the solution for 10 minutes at 4000 rpm. If the solution is still not clear, centrifuge an additional 10 minutes. Should the solution remain hazy, then it should be discarded as being incapable of accurate measurement. If, however, and this is the case most of the time, a clear solution is obtained, it is submitted for testing in a HunterLab ColorQuest Sphere Spectrocolorimeter. A transmission cell having a 20-mm transmission length is used. The colorimeter is set to “Delta E-lab” to report color as ΔE and to give color values for “L”, “a” and “b”. Product color is determined as total color difference ΔE using Hunter L, a, and b scales for the 10% by weight concentrations of the product in chlorobenzene versus chlorobenzene according to the formula:

[0087] ΔE=[(ΔL)²+(Δa)²+(Δb)²]^½

[0088] DSC Values. DSC values were obtained with a TA Instruments DSC Model 2920. Samples were heated from 25° C. to 400° C. at 10° C/min under nitrogen.

[0089] Thermogravimetric Analysis. Thermogravimetric analysis (TGA) is also used to test the thermal behavior of the brominated styrenic polymers of this invention. The TGA values are obtained by use of a TA Instruments Thermogravimetric Analyzer. Each sample is heated on a Pt pan from 25° C. to about 600° C. at 10° C./min with a nitrogen flow of 50-60 mL/min.

[0090] Thermal Stability Test. To determine thermal stability and estimate the corrosive potential of a sample, the Thermal Stability Test is used. The test procedure, described in U.S. Pat. No. 5,637,650, is used in the following manner. Each sample is run in duplicate. A 2.00±0.01 g sample is placed into a new clean 20×150 mm test tube. With a neoprene stopper and Viton® fluoroelastomer tubing, the test tube is connected to a nitrogen purge line with exit gas from the test tube being passed successively through subsurface gas dispersion frits in three 250-mL sidearm filter flasks each containing 200 mL of 0.1 N NaOH and 5 drops of phenolphthalein. With a constant nitrogen purge at 0.5 SCFH, the test tube is heated at 300° C. in a molten salt bath (51.3% KNO₃/48.7% NaNO₃) for 15 minutes followed by 5 minutes at ambient temperature. The test tube containing the sample is then replaced with a clean dry test tube, and the apparatus is purged with nitrogen for an additional 10 minutes with the empty test tube in the 300° C. salt bath. The test tube, tubing and gas dispersion tubes are all rinsed with deionized water, and the rinse is combined quantitatively with the solutions in the three collection flasks. The combined solution is acidified with 1:1 HNO₃and titrated with 0.01 N AgNO₃using an automatic potentiometric titrator (Metrohm 670, 716, 736, or equivalent). Results are calculated as ppm HBr, ppm HCl, and ppm HBr equivalents as follows:

[0091] ppm HBr=(EP 1)(N)(80912)/(sample wt.)

[0092] ppm HCl=(EP 2−EP 1)(N)(36461)/(sample wt.)

[0093] ppm HBr equivalents=(EP 2)(N)(80912)/(sample wt.)

[0094] where EP(x)=mL of AgNO₃used to reach end point x; and N=normality of AgNO₃. The tubing is thoroughly dried with nitrogen before the next analysis. Each day before the first sample, three empty clean test tubes are run as blanks to assure there is no residual hydrogen halide in the system.

[0095] GPC Weight Average Molecular Weights. The M, values were obtained by GPC using a Waters model 510 HPLC pump and, as detectors, a Waters Refractive Index Detector, Model 410 and a Precision Detector Light Scattering Detector, Model PD2000. The columns were Waters, μStyragel, 500Å, 100,000Å and 100,000 Å. The autosampler was a Shimadzu, Model Sil 9A. A polystyrene standard (M_w=185,000) was routinely used to verify the accuracy of the light scattering data. The solvent used was tetrahydrofuran, HPLC grade. The test procedure used entailed dissolving 0.015-0.020 g of sample in 10 mL of THF. An aliquot of this solution is filtered and 50 μL is injected on the columns. The separation was analyzed using software provided by Precision Detectors for the PD 2000 Light Scattering Detector.

[0096] The calculated theoretical M_wvalues were obtained in accordance with the equation: $\mathrm{Theoretical}{M}_w\mathrm{BrPS}=\frac{M_w\mathrm{PS}}{1-\left(\mathrm{wt}\%\mathrm{Br}\right)\left(0.01\right)}$

[0097] Melt Flow Index Test. To determine the melt flow index of the brominated styrenic polymers of this invention, the procedure and test equipment of ASTM Test Method D1238-99 are used. The extrusion plastometer is operated at 270 ° C. and 2.16 kg applied pressure. The samples used in the tests are composed of 50 parts by weight of antimony oxide, a calculated quantity in the range of about 200 to about 250 parts by weight of the brominated styrenic polymer that will provide a final blend containing 15.0 wt % Br based on the Br content of the brominated styrenic polymer, and sufficient glass-filled nylon 6,6 (Zytel polymer, from DuPont) to give a total of 1000 parts by weight.

[0098] As used throughout this application, “PS” is used interchangeably with and meant to designate polystyrene, while “Sty” means styrene. The term “M_w” means weight average molecular weight as determined by GPC (light scattering detector) described infra.

[0099] Substrate Polymer, Other Components, Proportions

[0100] Particular thermoplastics with which the foregoing brominated styrenic polymers can be blended pursuant to further embodiments of this invention include polyethylene terephthalate, polybutylene terephthalate, polycyclohexylene dimethylene terephthalate, polytrimethylene terephthalate, blends or mixtures of two or more of these, and analogous copolymeric thermoplastic polyesters, especially when filled or reinforced with a reinforcing filler such as glass fiber. Preferred thermoplastic polyesters are polyethylene terephthalate and polybutylene terephthalate. Polyamide thermoplastics, such as polyamide 6, polyamide 6,6, polyamide 12, etc., again preferably when glass filled, can also be effectively flame retarded in like manner. Other thermoplastic polymers that can be effectively flame retarded by addition of a brominated styrenic polymer of this invention include polystyrenes, high impact polystyrenes, polyolefins, ABS, MABS, SAN, aromatic polycarbonates, polyphenylene ethers, and polymer blends such as aromatic polycarbonate-ABS blends, polyphenylene ether-polystyrene blends, and similar substances. Conventional additives, such as flame retardant synergists, antioxidants, UV stabilizers, pigments, impact modifiers, fillers, acid scavengers, blowing agents, and the like, can be included with the formulations as is appropriate. Preferred polymer blends of this invention do contain a flame retardant synergist or glass fiber filler or reinforcement, and most preferably both a synergist, and a reinforcing fiber and/or filler.

[0101] The brominated styrenic polymer flame retardants of this invention are used in flame retardant amounts, which typically are within the range of from about 5 to about 20 wt %, the wt % being based on the total weight of the thermoplastic polymer formulation or blend. When used, the amount of reinforcing fillers such as glass fiber will typically be in the range of up to about 50 wt % based on the total weight of the finished composition. The amount of flame retardant synergist, when used, such as antimony trioxide, antimony pentoxide, sodium antimonate, potassium antimonate, iron oxide, zinc borate, or analogous synergist generally will be in the range of up to about 12 wt % based on the total weight of the finished composition. Departures from the foregoing ranges of proportions are permissible whenever deemed necessary or desirable under the particular circumstances at hand, and such departures are within the scope and contemplation of this invention.

[0102] Masterbatch compositions wherein the components except for the substrate thermoplastic polymer are in suitable relative proportions but are blended in a smaller amount of the substrate polymer, are also within the scope of this invention. Thus this invention includes compositions which comprise at least one thermoplastic polymer such as a polyalkylene terephthalate or a nylon polymer or a high impact polystyrene with which has been blended a brominated styrenic polymer preferably a brominated polystyrene) of this invention in a weight ratio (substrate polymer:brominated polystyrene) in the range of, say, 1:99 to 70:30. Such masterbatch blends need not, but may also contain filler or reinforcing fiber and/or at least one flame retardant synergist such as iron oxide, zinc borate, or preferably an antimony oxide synergist such as antimony trioxide, antimony pentoxide, sodium antimonate, or potassium antimonate. Typical examples of reinforcing agents or fillers that can be used include low-alkali E-glass, carbon fibers, potassium titanate fibers, glass spheres or microballoons, whiskers, talc, wollastonite, kaolin, chalk, calcined kaolin, and similar substances. Sizing agents can be used with such reinforcing agents or fillers, if desired. A number of suitable glass-filled polyalkylene terephthalates or nylon molding compositions are available on the open market, and these can be used in preparing the compositions of this invention.

[0103] Also provided by this invention are additive blends composed of a brominated styrenic polymer of this invention and a synergist such as, for example, a blend of 75 parts by weight of a brominated polystyrene and 25 parts by weight of a synergist such as antimony trioxide, antimony pentoxide, sodium antimonate, potassium antimonate, iron oxide, zinc borate, or analogous synergist. Typically such blends will contain in the range of about 70 to about 98 parts by weight of the brominated polystyrene and about 30 to about 2 parts by weight of the synergist, with the total of the two components being 100 parts by weight. Suitable amounts of other suitable additive components can also be included in such additive blends.

[0104] Various known procedures can be used to prepare the blends or formulations constituting such additional compositions of this invention. For example the polyalkylene terephthalate polymer or a nylon polymer and the brominated styrenic polymer such as brominated polystyrene and any other components or ingredients to be incorporated into the finished blend can be blended together in powder form and thereafter molded by extrusion, compression, or injection molding. Likewise the components can be mixed together in a Banbury mixer, a Brabender mixer, a roll mill, a kneader, or other similar mixing device, and then formed into the desired form or configuration such as by extrusion followed by comminution into granules or pellets, or by other known methods.

[0105] The following Examples are presented for purposes of illustration and are not to be construed as imposing limitations on the scope of the invention.

[0106] Examples 1-3 give preferred general procedures for producing brominated polystyrenes of this invention in which high melt flow is not required.

[0107] A mixture of 770.0 g bromochloromethane (BCM, 9 ppm water) and 2.775 g powdered AlCl₃was prepared in a 5-L jacketed glass reactor equipped with a mechanical paddle stirrer, condenser, and thermowell. A jacketed glass mixing tee was mounted on an inlet port on the reactor to which bromine (533.35 g, 3.337 mole) and a solution of 134.00 g (1.287/n mole) polystyrene (Mitsubishi Kasei Polytex, M_w=270,000) in 1204 g BCM were pumped at average rates of 8.74 g/min and 20.27 g/min, respectively. The reactor and mixing tee were cooled with a circulating glycol bath to maintain a temperature of 0° C. to 2° C. throughout the 1 hour feed time and subsequent 1 hour cook. The reaction mixture was then washed with water and neutralized with a mixture of aqueous sodium gluconate, sodium sulfite, and sodium hydroxide. After diluting the organic phase with additional BCM (1450 g), the solution was added dropwise to 1.8 L hot (90° C.-94° C.) water containing 0.25 g dioctyl sulfosuccinate sodium salt (surfactant) to precipitate the product and distill the solvent. The slurry was filtered and the off-white solid was washed with water. Drying to constant weight at 150° C. gave 389.8 g.

[0108] A 7.209 g (54.1 mmol) portion of powdered aluminum chloride was suspended (stirred at 250 rpm) in 1549.83 g of dry (10 ppm water) bromochloromethane (BCM) in a 5-L jacketed reaction flask cooled to 0° C. by a circulating glycol bath. A 10.00 wt % solution of PS (Styron 612 polystyrene; M_w=190,000; The Dow Chemical Company) (360.96 g, 3.4657/n mol) in dry BCM (3250.44 g) was prepared in a second 5-L flask. The PS used was Dow Styron® 612 which had a M_wof 190,000. The PS solution was pumped from the bottom valve of this feed reservoir to a jacketed, glycol-cooled mixing tee mounted on the reaction flask. At the same time, bromine was pumped from a tared feed reservoir to the same mixing tee where it combined with the polystyrene solution before dropping into the stirred catalyst suspension in the reaction flask. Two Masterflex® 7550-90 pumps were used. The PS feed system used an all-Teflon feed line with pump head 77390 operating at a constant speed of 60 rpm. This provided a constant feed rate of 21.02/n mmol PS/min (21.89 g/min). The bromine feed system used a combination of Teflon and Viton tubing with pump head 7518-10 operating at a rate of 70.05 mmol/min for the first 18 min, 38.80 mmol/min for 18-23 min, and 56.75 mmol/min for 23-165 min. Both feeds ended at 165 min. The overall mole ratio of Br₂/PS was 2.70. A rinse of 260.95 g of dry BCM was used for the PS solution feed system to assure complete transfer of the polymer to the reaction flask. The reaction temperature was maintained at 0° C. to 4° C. throughout the addition and subsequent 2.3 hour cook period (with nitrogen purge of the reactor overhead). The weight increase for the caustic exit gas scrubber was 665.4 g (87.8% of theory for HBr). The catalyst was deactivated by addition of 125.0 g of a 10 wt % aqueous solution of sodium gluconate. A 63.41 g portion of 10 wt % aqueous sodium sulfite was added, and the pH was adjusted to 14 by addition of 423.0 g of 10 wt % aqueous NaOH. After dilution with BCM (1334.6 g), the organic phase was separated and then washed with water (1011.8 g). The product was recovered from the organic phase by addition to vigorously stirred hot (90° C.-94° C.) water to which was added 1.23 g of the sodium salt of dioctyl sulfosuccinate. The solvent distilled from the hot water leaving a slurry of brominated polystyrene product in water. After suction filtering, the off-white solid was rinsed with water and dried to a constant weight of 1085.98 g (97.9% yield) in a vacuum oven (150° C./2 torr/5 hr). The ionic bromine content of the brominated polystyrene so produced was only 88 ppm by weight.

[0109] The procedure of Example 2 was followed except that: a 2-L flask and 40 g of the Styron 612 polystyrene were used; the AlCl₃wt % (based on polystyrene) was 2.0 wt %; the feed mole ratio of bromine to polystyrene was 3.33; the total equivalents of bromine was 2.78; the temperature range was 0° C. to 5° C.; the feed times for the bromine/polystyrene was 32 min/38 min; and the cook time was 150 minutes.

[0110] Example 4, wherein all parts are by volume unless otherwise specified, illustrates a preferred purification process for removing ionic bromine from brominated polystyrene during the course of preparing the polymer.

[0111] A brominated polystyrene reaction mass (1500 parts), formed by reacting bromine with a 10 wt % solution of Styron 612 polystyrene in bromochloromethane (BCM) using aluminum chloride as catalyst, was quenched in 450 parts of water, and thoroughly mixed for 15 minutes. A sample of the quenched reaction mass (Sample A) was taken for use in the purification process described below. The aqueous and organic phases were allowed to settle and the aqueous phase was removed by decantation. The organic phase was then brought to pH 12 by the addition of 50 parts of fresh water and 25 parts of 25 wt % sodium hydroxide solution. This mixture was thoroughly mixed. Any residual bromine was scavenged by addition to the mixture of 1.7 parts of 6.9 wt % sodium borohydride in 23 wt % aqueous sodium hydroxide solution, followed by thorough mixing. A sample of the resultant organic phase (Sample B) was taken for recovery of the brominated polystyrene without use of the following purification process.

[0112] Application of the purification process to Sample A was performed as follows: Sample A was poured into a 1000 mL glass separatory funnel. The aqueous and organic phases were allowed to separate for 5 minutes. The organic phase was removed from the bottom of the funnel (325.2 grams). The aqueous layer was recovered (71.0 grams). The organic phase was separated into two equal halves and placed into two 8-ounce jars. Fresh water was placed into each jar for a second water wash (46.1 grams). This water level is equivalent to a ratio of 850 parts of water to 1500 parts of reaction mass. Both jars were shaken for 30 minutes on a Burrell Wrist Action Shaker. The contents of both jars were poured into and combined in a 1000 mL separatory funnel and allowed to separate for 5 minutes. The organic phase was recovered from the bottom (319.5 grams), and 95.3 grams of aqueous phase remained in the funnel. Fresh water (12.8 grams) was added to the organic phase to assist in pH reading using strips of pH indicator paper. The pH of the organic phase was 5. The pH was raised to 14 by the addition of 25% by weight aqueous sodium hydroxide solution (2.4 grams). Excess bromine was scavenged by the addition of 6.9 wt % sodium borohydride in 23 wt % aqueous sodium hydroxide solution (0.5 gram). The brominated styrene product from Sample A was recovered by precipitation into a mixture formed from 1500 grams of water and 12.6 grams of 25% by weight aqueous sodium hydroxide solution. In conducting this precipitation operation, the water-sodium hydroxide mixture was in a 3000 mL glass reactor, with baffles, and was heated to 100° C. The vessel was stirred by an agitator set on 500 rpm. The organic phase was fed into this reactor by a peristaltic pump, set on 42 rpm through ⅛″ polypropylene tubing into the water. The feed point was approximately ½″ underneath the water surface. The BCM was condensed and removed overhead. After the organic phase was fed, the water temperature was allowed to return to 100° C. to remove any residual BCM and then cool. The brominated polystyrene product was vacuum filtered in a 2000 mL fritted glass filter. It was washed three times with approximately 1000 mL of warm water. The solids were dried in a vacuum oven at 140° C. overnight. The ionic bromine level detected in the final brominated polystyrene product from Sample A was 222 ppm.

[0113] The brominated polystyrene product from Sample B, without use of the above purification process, was recovered by use of the foregoing precipitation procedure. The precipitation used 1500 grams of water and 13.0 grams of 25% by weight sodium hydroxide aqueous solution followed by three washings with warm water. The ionic bromine level detected in the final brominated polystyrene product recovered from Sample B was 1810 ppm.

[0114] In carrying out the purification process illustrated in Example 4, effective use can be made of coalescing filters and/or a liquid-liquid extraction column. The principles involved in the design and operation of such equipment is known and reported in the literature. Anyone interested in pursuing such information can refer, for example, to I. Bartik, Liquid/Liquid Separation Through The Use of Coalescence,a paper presented on Feb. 8, 1977 at The Filtration Society, New England Chapter, Sturbridge, Massa. 01566; and McCabe and Smith, Unit Operations of chemical Engineering,Third Edition, McGraw-Hill Book Company, pages 619-627; or other similar sources. In using a liquid-liquid extraction tower the water should be introduced into the column below the incoming countercurrent flow of the crude organic phase to the tower, so that the water extract is taken from the upper portion of the tower and the extracted organic phase is removed from the lower portion of the tower.

[0115] Comparative Examples CE-1 and CE-2 describe the preparation of brominated polystyrene in accordance with the teachings of U.S. Pat. No. 5,532,322, which issued in 1996.

[0116] A solution of 75.10 g (0.721/n mole) of polystyrene (Mitsubishi Kasei Polytex, M_w=270,000) in 750 g of 1,2-dichloroethane (EDC, containing 12 ppm water) was prepared in a 5-L jacketed glass reactor equipped with a mechanical paddle stirrer, condenser, and thermowell. The temperature of the reaction was controlled with an ethylene glycol circulating bath on the reactor jacket. After cooling to 15° C., 11.03 g of antimony (III) oxide was added to the polystyrene solution. A previously prepared solution of 149.7 g (0.937 mole) bromine and 66.3 g (0.935 mole) chlorine in 505 g cold (−5° C.) EDC was added to the reactor under the liquid surface through a diptube attached to the cooled bromine chloride feed reservoir. The reaction temperature was slowly increased from 10° C. to 25° C. during the 2 hour addition. The mixture was then held at 30° C. until hydrogen halide evolution was complete (1.5 hr) as indicated by an end of the weight gain of the caustic scrubber on the exit gas line from the reactor. The reaction mixture was washed with water and neutralized with aqueous sodium sulfite and caustic. The organic phase was then added dropwise to 3.5 L methanol to precipitate the product. The slurry was filtered and the solid was washed with methanol. After vacuum drying at 150° C., the light yellow solid (product 1) weighed 203.7 g.

[0117] Comparative Example CE-1 was repeated using 230.8 g (2.00 mole) commercial bromine chloride with 80.20 g (0.770/n mole) polystyrene and 11.77 g Sb₂O₃. The water washed and neutralized organic phase was divided into two equal portions. One portion was added to 1.5 L of methanol as in Example CE-1 to obtain 101.6 g of light yellow solid (product A) after drying to constant weight at 1500° C. The other portion was added dropwise to 1.9 L of hot (89° C.-94° C.) water to precipitate the product and distill the solvent. The dry light yellow solid (product B) weighed 100.3 g.

[0118] In Table 1 a compilation of the properties of the brominated polystyrene products produced in Examples 1-3 and Comparative Examples CE-1 and CE-2 is given. In addition, the properties of Pyro-Chek 68PB flame retardant of Ferro Corporation are given. Pyro-Chek 68PB flame retardant is believed to be produced in accordance with the teachings of U.S. Pat. No. 4,352,909.

[0119] Examples 5, 6, and 7 illustrate additional procedures by which brominated polystyrenes of this invention can be prepared, again where high melt flow is not required.

[0120] A 0.910 g (6.82 mmol) portion of powdered aluminum chloride was suspended (stirred at 250 rpm) in 190 g of dry (13 ppm water) bromochloromethane (BCM) in 1-L jacketed flask cooled to 0° C. by circulating glycol bath. A 419.86 g portion of a 10.00 wt % solution of Styron 612 polystyrene (403.1/n mmol) in dry BCM was pumped at a constant rate of 8.46 g/min (8.13 mmol/min) to a jacketed, glycol-cooled mixing tee mounted on the reaction flask. At the same time, bromine was pumped at a constant rate of 6.09 g/min (38.1 mmol/min) to the same mixing tee where it combined with the polystyrene solution (feed mole ratio of Br₂/PS is 4.69) before dropping into the stirred catalyst suspension in the reaction flask. The bromine feed was stopped after 30.0 min (1143.5 mmol) and the polystyrene solution feed was stopped after 49.6 minutes (overall mole ratio of Br₂/PS is 2.84). A rinse of 160 g of dry BCM was used for the polystyrene solution feed system to assure complete transfer of the polymer to the reaction flask. The reaction temperature was maintained at 0° C.-5° C. throughout the addition and subsequent 2 hr cook period. The catalyst was deactivated by addition of 16.4 g of 10 wt % aqueous solution of sodium gluconate, and pH was adjusted to 14 by addition of 60.7 g of 10 wt % aqueous NaOH. The reaction mixture was washed with 10 wt % aqueous sodium sulfite followed by a water wash. The product was recovered from the organic phase by addition to vigorously stirred hot (90° C.) water containing 0.02 wt % dioctyl sulfosuccinate sodium salt surfactant. The solvent is distilled from the hot water leaving a slurry of the brominated polystyrene product in water. After filtering, the powdery solid was rinsed with water and dried to constant weight in a vacuum oven (150° C./2 torr/5 hr). The dry solid weighed 127.08 g (95% yield). The product contained 69.6 wt % total Br. In the thermal stability test referred to above, the product evolved 174 ppm of HBr in 15 minutes at 300° C. The HunterLab solution color (10 wt % in chlorobenzene) values were L=94.58, a=−2.79, b=17.29, Delta E=18.34.

[0121] A Y-shaped mixing apparatus having a cooling jacket was equipped with 2 feed lines, each connected to a pump. One of the feed lines was for delivering bromine and the other was for delivering a PS (Styron 612 polystyrene) and BCM solution. Bromine (93.3 g, 31.3 mL or 0.583 mole), delivered at a rate of 1 mL/min (19.4 mmol/min), and a PS/BCM solution (22.4 g PS, 0.215 mol and 97 mL or 194 g of anhydrous BCM), delivered at 4 mL/min (7.17 mmol/min), were fed simultaneously from their respective feed lines into the cooled (5° C.) Y-mixing apparatus. The resultant intimate mixture from the mixing apparatus was then fed into a cooled (5° C.) suspension of 0.45 g (2 wt % based on PS) of powdered aluminum chloride in 49 mL (98 g) of anhydrous BCM. Evolved HBr was scrubbed by a caustic solution during the reaction. The feeds were complete in 35 minutes and the mixture was cooked for 2 hours at 5° C. After water and sodium sulfite washes, solid BrPS was isolated by precipitating from 500 mL of hot (90° C.) water as described above. A total of 66 g of BrPS (97% yield) was obtained. The product contained 68.4 wt % total Br. In the thermal stability test referred to above, the product evolved 71 ppm of HBr in 15 minutes at 300° C. The HunterLab solution color (10 wt % in chlorobenzene) values were L=96.74, a =−1.90, b=15.99, Delta E=16.44.

[0122] A 0.910 g (6.82 mmol) portion of powdered aluminum chloride is suspended (stirred at 250 rpm) in 190 g of dry (13 ppm water) bromochloromethane (BCM) in 1-L jacketed flask cooled to 0° C. by circulating glycol bath. A 419.86 g portion of a 10.00 wt % solution of Styron 612 polystyrene (403.1/n mmol) in dry BCM is pumped at a constant rate of 8.46 g/min (8.13 mmol/min) to a jacketed, glycol-cooled mixing tee mounted on the reaction flask. At the same time, bromine is pumped at a constant rate of 6.09 g/min (38.1 mmol/min) to the same mixing tee where it is combined with the polystyrene solution (feed mole ratio of Br₂/PS is 4.69) before dropping into the stirred catalyst suspension in the reaction flask. The bromine feed is stopped after 30.0 min (1143.5 mmol) and the polystyrene solution feed is stopped after 30 minutes (overall mole ratio of Br₂/PS is 2.84). A rinse of 160 g of dry BCM is used for the polystyrene solution feed system to assure complete transfer of the polymer to the reaction flask. The reaction temperature is maintained at 0° C.-5° C. throughout the addition and subsequent 45 minute cook period. The catalyst is deactivated by addition of 16.4 g of water. The crude organic and aqueous phases are allowed to settle, and the aqueous acidic phase is removed. Then the pH is adjusted to 14 by the addition of 10 wt % aqueous NaOH, and sodium borohydride is added to scavenge any excess bromine. The product is then recovered from the organic phase by addition to vigorously stirred hot (90° C.) water. The solvent is distilled from the hot water leaving a slurry of the brominated polystyrene product in water. After filtering, the powdery solid is rinsed with water and dried to constant weight in a vacuum oven (150° C./2 torr/5 hr).

[0123] Examples 8-21 illustrate additional preferred procedures for producing brominated polystyrenes of this invention having desirable thermal stabilities and good color characteristics but in which high melt flow properties are not required.

[0124] The following procedure was used in these Examples: A mixture of 1.44 g (10.8 mmol) of aluminum chloride (Aldrich, anhydrous) and 310 g of dry (10-60 ppm water after drying over molecular sieves) bromochloromethane (BCM) was stirred at 350 rpm with a paddle of Teflon® polymer in a 1-L three-necked jacketed round bottom flask. The flask contents were cooled to the desired temperature by circulating chilled ethylene glycol through the jacket. A 10 wt % solution of Dow Styron 612 polystyrene (72.2 g; 0.69 equivalents) in dry BCM (650 g) was charged to a separate vessel (500 mL graduated addition funnel). The polystyrene solution was pumped from the bottom of this feed reservoir to a vacuum jacketed mixing tee mounted on the reaction flask. The tee was maintained at the same temperature as the reaction mixture by circulating the ethylene glycol exiting from the flask to the tee. As the polystyrene solution was pumped from the reservoir, bromine (295.5 g; 1.85 mol) was simultaneously pumped from a 125-mL graduated addition funnel to the same mixing tee where it combined with the polystyrene solution. The resulting red solution flowed through the jacketed, spiral column (approximately 12″ in length) and exited above the surface of the stirred catalyst suspension. Two Masterflex pumps were used for the feed to the mixing tee. The polystyrene system used an all Teflon line with a Cole-Palmer 77390 pump head. The bromine feed system used a combination of Teflon and Viton tubing with the latter being used with a Masterflex 7518-10 pump head. Both feeds ended in approximately 32-35 minutes. Constant attention to feed rates was necessary in order to achieve complete addition simultaneously. The overall mole ratio of Br₂/PS was 2.7. A rinse of 57 g of dry BCM was used for the polystyrene solution feed system to assure complete transfer of the polymer to the reaction flask. After the addition was complete, the reaction was stirred at temperature for 45 minutes while being swept with nitrogen and was then quenched by the addition of 13 g of a 10 wt % solution of sodium sulfite. During the quench the material was stirred at 450 rpm and was stirred at this rate for 5 minutes. The reaction color changed from red/brown to a cream (light tan) during the sulfite addition. The reaction was allowed to stand for 5 minutes and the phases were separated using a bottom valve on the reaction flask. After removing the aqueous phase from the reactor, the organic layer was returned to the reactor and the pH was adjusted to 14 with the use of 10 wt % aqueous NaOH (100-200 g). Additional BCM (267 g) was added, the mixture was transferred to a separatory funnel, and the phases were allowed to separate. Product was recovered from the organic phase by addition to hot water as follows. A 2-L three-necked creased flask equipped with a mechanical stirrer, 125 mL addition funnel, thermometer, and Dean-Stark trap with a condenser was charged with 700 mL of water and heated to 92-94° C. with a heating mantle. The addition funnel was filled with the contents from the bottom phase of the separatory funnel. The feed rate from the addition funnel was controlled so that the condenser on the Dean-Stark trap was not overloaded and so that the water temperature did not fall below 91° C. BCM and some water were removed overhead while the product precipitated in the water as white to yellowish-white solids. The addition funnel was refilled as necessary to have a continuous flow of material to the flask. After the addition was complete, the slurry was stirred at temperature for about 10 minutes to ensure complete removal of BCM. The slurry was allowed to cool to about 65° C. and collected on a Buchner funnel using suction filtration through #2 filter paper. About 300 mL of hot water was used to rinse the flask and the filter cake. The solids were transferred to a 2-L beaker, thoroughly mixed with 400 mL of water and reisolated by suction filtration. The solids were air dried overnight and then dried at 150° C. in a vacuum oven (1-5mm Hg) until a constant weight (180-200 g) was achieved. The product was powdered with a mortar and pestle prior to analysis (see Table IV).

[0125] The ionic bromine content of the brominated polystyrene formed in Example 14 was measured and found to be only 320 ppm by weight.

[0126] Commonly-owned application Ser. No.09/066,172, filed Apr. 24, 1998, describes processes in which a suitable amount of aqueous base is employed to improve the thermal stability of the resultant brominated polystyrene. It is to be noted that the use of such processes, while desirable, is not required pursuant to this invention, as the excellent results referred to hereinabove were achieved without using brominated polystyrene formed in this way. Thus the process procedures which are fully described in this commonly-owned copending application, constitute optional, but entirely suitable procedures for producing brominated polystyrenes of the present invention.

[0127] Inclusion of the suitable amount of inorganic alkali metal base such as NaOH or KOH into the brominated polystyrenes of Examples 8-21 is preferably accomplished substantially in the manner described in Example 22, infra, by utilizing a suitable excess of aqueous NaOH (or KOH) when precipitating the brominated polystyrene from BCM, and either eliminating the final water wash step or substituting an aqueous NaOH (or KOH) solution as the final wash. Alternatively, and less preferably, brominated polystyrenes formed as described in Examples 8-21 in finely-divided or powder form can be powder blended with suitable quantities of powdered alkali metal base such as sodium hydroxide, sodium acetate, or potassium hydroxide.

[0128] The procedure of Example 1 is repeated and in the step wherein the reaction mixture is washed with water and neutralized with a mixture of aqueous sodium gluconate, sodium sulfite, and sodium hydroxide, the amount of the aqueous sodium hydroxide is such that a dried sample of the brominated polystyrene composition produced in the process, when subjected to the following pH determination procedure, gives an aqueous extract having a pH of 9.3. The procedure for determining pH of the brominated polystyrene composition is as follows: Place in a beaker 1 gram to 1.5 grams of a representative sample, weighed to the nearest 0.1 gram, and dissolve same in 50 mL of BCM. Then add 50 mL of water which has been boiled to remove carbon dioxide and has a pH of 7. Vigorously stir the resultant mixture with a magnetic stirrer such that the two liquid phases are intimately mixed for 2 to 5 minutes. Then reduce the stirrer speed such that the two phases separate in the beaker, and lower the pH electrode in the upper layer only. Measure the pH of the upper layer using a Hach EC-10 pH meter (or equivalent) that has been calibrated the same day.

[0129] Examples 23 through 33 illustrate the preparation of brominated polystyrenes of this invention having properties such as the combination of great resistance to evolution of HBr in the Thermal Stability Test and consequent low corrosivity, extremely low ΔE color values, and in many cases very desirable melt flow properties, which so far as is presently known is a combination of properties which has never before been achieved in a brominated polystyrene produced by bromination of a pre-existing polystyrene. In Examples 23-25 the bromination was effected with 2.00 equivalents of bromine. In Examples 26-29 the bromination was effected with 2.27 equivalents of bromine. In Examples 30-33, 2.70 equivalents of bromine were used in the bromination.

[0130] A 2.280 g (17.0 mmol) portion of aluminum chloride was suspended in 587 g of dry (<15 ppm water) bromochloromethane in a 1-L, 5-necked, jacketed reaction flask cooled to −7° C. by a circulating glycol bath. A 451.1 g portion of a 30 wt % solution (135.3 g PS, 1.30/n mol) of polystyrene (Pressure Chemical Co., Pittsburgh, Pa., lot 50110, anionic PS, Mw 2,097) in dry BCM was charged to a 500-mL graduated cylinder in a dry box. The graduated cylinder was then set up to pump the PS solution from the cylinder to a jacketed, glycol-cooled mixing tee mounted on the reaction flask. Bromine (415.3 g, 2.60 moles, 2.00 equivalents) was charged to a 250-mL graduated cylinder and set up to pump the bromine to the same mixing tee as the PS solution. Both streams were cooled separately by the mixer before combining at the bottom of the apparatus and dropping into the bromination flask. Both feeds were started at the same time and were both completed in 58 min. A rinse of 105 g of dry BCM was used for the PS solution feed system to assure complete transfer of the polymer to the reaction flask. The reaction temperature was maintained at −2° C. to −4° C. throughout the addition and subsequent 15 min cook period (with nitrogen purge of the reactor overhead). The catalyst was deactivated by addition of 46 g of water. A 100 g portion of 10 wt % aqueous sodium sulfite was then added to removed any residual bromine. The organic phase was separated and then washed with water (4×1 L) until neutral. The product was recovered from the organic phase by addition to vigorously stirred hot (98° C.) water. The solvent distilled from the hot water leaving a slurry of the brominated polystyrene product in water. After suction filtering, the white solid was rinsed with water and dried to a constant weight of 330.5 g (96% yield) in a vacuum oven (110° C./2 torr). Product analyses appear in Table V.

[0131] Example 23 was repeated using anionic PS (Pressure Chemical Co., lot 30525) of 4,000 Mw. Product weight was 333.2 g (97% yield). Analytical results are in Table V.

[0132] Example 23 was repeated using anionic PS (Sartomer Technologies, Inc., West Chester, Pa., lot 626132) of 25,800 Mw. Product weight was 326.0 g (95% yield). Analytical results are in Table V.

[0133] A 2.145 g (16.1 mmol) portion of aluminum chloride was suspended in 588 g of dry (<15 ppm water) bromochloromethane in a 1-L, 5-necked, jacketed reaction flask cooled to −7° C. by a circulating glycol bath. A 418.6 g portion of a 30 wt % solution (125.6 g PS, 1.21/n mol) of polystyrene (Pressure Chemical Co., lot 50110, anionic PS, Mw 2,097) in dry BCM was charged to a 500-mL graduated cylinder in a dry box. The graduated cylinder was then set up to pump the PS solution from the cylinder to a jacketed, glycol-cooled mixing tee mounted on the reaction flask. Bromine (437.5 g, 2.74 moles, 2.27 equivalents) was charged to a 250-mL graduated cylinder and set up to pump the bromine to the same mixing tee as the PS solution. Both streams were cooled separately by the mixer before combining at the bottom of the apparatus and dropping into the bromination flask. Both feeds were started at the same time and were both completed in 59 min. A rinse of 101 g of dry BCM was used for the PS solution feed system to assure complete transfer of the polymer to the reaction flask. The reaction temperature was maintained at −2° C. to −4° C. throughout the addition and subsequent 15 min cook period (with nitrogen purge of the reactor overhead). The catalyst was deactivated by addition of 50 g of water. A 117 g portion of 10 wt % aqueous sodium sulfite was then added to removed any residual bromine. The organic phase was separated and then washed with water (4×1 L) until neutral. The product was recovered from the organic phase by addition to vigorously stirred hot (98° C.) water. The solvent distilled from the hot water leaving a slurry of the brominated polystyrene product in water. After suction filtering, the white solid was rinsed with water and dried to a constant weight of 334.1 g (97% yield) in a vacuum oven (110° C./2 torr). Product analyses appear in Table V.

[0134] Example 26 was repeated using anionic PS (Pressure Chemical Co., lot 30525) of 4,000 Mw. Product weight was 342.2 g (98% yield). Analytical results are in Table V.

[0135] Example 26 was repeated using anionic PS (Pressure Chemical Co., lot 30) of 10,600 Mw. Product weight was 340.1 g (97% yield). Analytical results are in Table V.

[0136] Example 2A was repeated using anionic PS (Sartomer Technologies, Inc., lot 626132) of 25,800 Mw. Product weight was 338.1 g (97% yield). Analytical results are in Table V.

[0137] A 1.860 g (14.0 mmol) portion of aluminum chloride was suspended in 589 g of dry (<15 ppm water) bromochloromethane in a 1-L, 5-necked, jacketed reaction flask cooled to −7° C. by a circulating glycol bath. A 369.5 g portion of a 30 wt % solution ( 10.9 g PS, 1.06/n mol) of polystyrene (Pressure Chemical Co., lot 50110, anionic PS, Mw 2,097) in dry BCM was charged to a 500-mL graduated cylinder in a dry box. The graduated cylinder was then set up to pump the PS solution from the cylinder to a jacketed, glycol-cooled mixing tee mounted on the reaction flask. Bromine (460.8 g, 2.88 moles, 2.71 equivalents) was charged to a 250-mL graduated cylinder and set up to pump the bromine to the same mixing tee as the PS solution. Both streams were cooled separately by the mixer before combining at the bottom of the apparatus and dropping into the bromination flask. Both feeds were started at the same time and were both completed in 63 min. A rinse of 100 g of dry BCM was used for the PS solution feed system to assure complete transfer of the polymer to the reaction flask. The reaction temperature was maintained at −3° C. to −4° C. throughout the addition and subsequent 15 min cook period (with nitrogen purge of the reactor overhead). The catalyst was deactivated by addition of 40 g of water. A 98 g portion of 10 wt % aqueous sodium sulfite was then added to removed any residual bromine. The organic phase was separated and then washed with water (4×1 L) until neutral. The product was recovered from the organic phase by addition to vigorously stirred hot (98° C.) water. The solvent distilled from the hot water leaving a slurry of the brominated polystyrene product in water. After suction filtering, the white solid was rinsed with water and dried to a constant weight of 331.9 g (97% yield) in a vacuum oven (115° C./2 torr). Product analyses appear in Table V.

[0138] Example 30 was repeated using anionic PS (Pressure Chemical Co., lot 30525) of 4,000 Mw. Product weight was 331.5 g (97% yield). Analytical results are in Table V.

[0139] Example 30 was repeated using anionic PS (Pressure Chemical Co., lot 30) of 10,600 Mw. Product weight was 329.9 g (97% yield). Analytical results are in Table V.

[0140] Example 30 was repeated using anionic PS (Sartomer Technologies, Inc., lot 626132) of 25,800 Mw. Product weight was 327.3 g (96% yield). Analytical results are in Table V.

[0141] It can be seen from the above that it is possible pursuant to this invention to provide brominated styrenic polymers such as brominated polystyrene which have a ΔE color value, measured using 10 wt % solutions in chlorobenzene, after exposure of the solutions to a temperature of 300° C. for 15 minutes, of less than about 25, and in many cases to less than about 22, and in some cases to less than about 19. In addition, brominated styrenic polymers such as brominated polystyrene can be formed which are further characterized in that the difference between (i) the ΔE color value, measured using 10 wt % solution in chlorobenzene, after exposing the brominated polystyrene polymer to a temperature of 300° C. for 15 minutes, and (ii) the ΔE color value, measured using 10 wt % solution in chlorobenzene, without subjecting the brominated polystyrene polymer to the temperature of 300° C. for 15 minutes, is less than about 23, in many cases less than about than about 19, and in some cases to less than about 16. The brominated polystyrenes all had DSC temperatures of 120° C. or above. It will also be seen that in most cases, the TGA temperature for a 1% weight loss, when the tests were conducted under nitrogen as the measurements are usually carried out, were above 340° C.

[0142] The vast superiority of the compositions of this invention is demonstrated by Comparative Examples CE-3 through CE-11. These Comparative Examples involve analyses performed in our laboratories on samples of brominated anionic polystyrenes of products made by another party in accordance with U.S. Pat. Nos. 4,352,909 and U.S. Pat. No. 5,723,549, and furnished by that party. The procedure used and reported by that party in making each of these samples is as given in Comparative Examples CE-3 through CE-11. Each such Comparative Example involved use of an anionic polystyrene differing in number average molecular weight from the others.

[0143] COMPARATIVE EXAMPLES CE-3-CE-11

[0144] A 300 g (2.88/n moles) portion of an anionic polystyrene (Pressure Chemical Co.) was dissolved in 2500 mL of 1,2-dichloroethane (EDC) in a 5-L resin flask. The flask was equipped with a mechanical stirrer, condenser, thermometer, and a jacketed, pressure-equalized addition funnel. A 37.5 mL portion of an EDC solution of antimony trichloride (0.4 g SbCl₃/mL) was added to the polymer solution, and the solution was cooled to 20° C. A bromine chloride solution composed of 1125 g EDC, 1125 g (9.752 moles) BrCl, and 16.2 g (0.10 mole) bromine was added continuously from the cooled addition funnel to the polymer solution in 3 hr at a pot temperature of 20° C. The mixture was held at 20° C. for approximately 1 hr, and then excess BrCl was neutralized with 20 wt % aqueous sodium bisulfite while keeping the temperature under 35° C. The mixture was transferred to a separatory funnel. The organic layer was removed and water washed three times. The pH of the third wash was adjusted to 7 by addition of saturated aqueous sodium bicarbonate. The organic phase was then added to vigorously stirred hot water in a Morton resin flask to flash off the solvent and obtain a slurry of brominated polystyrene in water. The product was collected by filtration and washed on the filter with water. After oven drying (80-100° C./10 torr/48 hr), the final product weight was 875 g (93% yield).

[0145] Table VI summarizes the results of the analytical data on the samples from Comparative Examples CE-3 through CE-11.

[0146] Comparative Example CE-12 still further demonstrates the eminent superiority of the brominated anionic polystyrenes of this invention. In this Comparative Example analyses were performed in our laboratories of a sample prepared by still another party utilizing the procedures described in EP 0 201 411 and furnished by that party. The reaction conditions used by that party in preparing the sample as reported by that party show that the product was formed by bromination of 25 pounds of an anionic polystyrene of 55,000 number average molecular weight in 300 pounds of methylene dichloride solvent with 98.5 pounds of bromine using 150 grams of ferric chloride as catalyst. The bromine was added over a period of 1 hour and 35 minutes, and the ride time thereafter was 2 hours and 30 minutes. The reaction was performed at temperatures in the range of 3.0 to 8.0. The first wash of the product was conducted with water containing 0.5 pound of sulfur dioxide. This sample was regarded by that party as representative of the capabilities of the process of EP 0 201 411. The results of the analyses on this comparative brominated anionic polystyrene are summarized in Table VII.

[0147] It is to be understood that the components referred to by chemical name or formula anywhere in the specification or claims hereof, whether referred to in the singular or plural, are identified as they exist prior to coming into contact with another substance referred to by chemical name or chemical type (e.g., another component, a solvent, or etc.). It matters not what preliminary chemical changes, transformations and/or reactions, if any, take place in the resulting mixture or solution as such changes, transformations, and/or reactions are the natural result of bringing the specified components together under the conditions called for pursuant to this disclosure. Thus the components are identified as ingredients to be brought together in connection with performing a desired operation or in forming a desired composition. Even though the claims hereinafter may refer to substances, components and/or ingredients in the present tense (“comprises”, “is”, etc.), the reference is to the substance, component or ingredient as it existed at the time just before it was first contacted, blended or mixed with one or more other substances, components and/or ingredients in accordance with the present disclosure. The fact that a substance, component or ingredient may have lost its original identity through a chemical reaction or transformation during the course of contacting, blending or mixing operations, if conducted in accordance with this disclosure and with the application of common sense and the ordinary skill of a chemist, is thus wholly immaterial for an accurate understanding and appreciation of the true meaning and substance of this disclosure and the claims thereof.

[0148] Each and every patent or publication referred to in any portion of this specification is incorporated in toto into this disclosure by reference, as if fully set forth herein.

[0149] This invention is susceptible to considerable variation in its practice. Therefore the foregoing description is not intended to limit, and should not be construed as limiting, the invention to the particular exemplifications presented hereinabove. Rather, what is intended to be covered is as set forth in the ensuing claims and the equivalents thereof permitted as a matter of law.