Method for Modifying the Properties of Rubbery Polymers of Conjugated Dienes

This invention relates to rubbery polymers of conjugated dienes and to a method for modifying their physical properties. In one aspect this invention relates to a method for reducing cold flow and increasing the viscosity characteristics of homopolymers of conjugated dienes and copolymers of conjugated dienes with monovinyl aromatic compounds. In still another aspect this invention relates to a method for modifying the properties of rubbery polymers of conjugated dienes by treating such dienes with a homogeneous olefin disproportionation catalyst.

In the preparation of rubbery polymers it is a common practice to blend together several batches of polymer in order to arrive at a polymer having certain desired physical properties. For example, batches of polymer having different values of Mooney viscosity can be blended to arrive at a desired value of Mooney viscosity; however, other properties of such a blend would have to be accepted as they result or be modified in some other manner. It must also be recognized that in making such a blend the resulting Mooney viscosity would not be higher than the highest component of the blend and the cold flow property value would not be less than the lowest cold flow value of a component of the blend. Thus, there is a definite limitation on the manipulation of the physical properties of rubbery polymers by blending different batches of such polymers.

Broadly the present invention is directed to a process for modifying physical properties of rubbery polymers of conjugated dienes by treating the polymers with a homogeneous olefin disproportionation catalyst, e.g., a homogeneous catalyst active for disporportionating propylene into ethylene and butenes.

This invention provides a method for modifying the properties of a conjugated diene polymer by treating it with a homogeneous olefin disproportionation catalyst. While it is not intended that the invention be limited to any particular reaction mechanism, it is believed that a redistribution of molecular weight occurs, and if the polymer contains side chain unsaturation, the treatment results in a considerable amount of long chain branching as well as cyclization with adjacent side chain unsaturation. It is also possible that graft polymerization will result, particularly when mixtures of conjugated diene polymers are utilized. These polymers can contain the same or different monomers.

Accordingly, the polymers treated in accordance with the invention exhibit modified cold flow when compared to the untreated polymers. The treated polymer cold flow can be increased or decreased, although the invention finds greater usefulness in decreasing cold flow. Additionally, the polymers exhibit a change in molecular weight as exhibited by inherent viscosity when compared to the untreated polymers; the change in inherent viscosity can be an increase, with corresponding increase in Mooney viscosity, or it can be a decrease, with corresponding decrease in Mooney viscosity. The direction of change (increase or decrease) in inherent viscosity is dependent on the nature and type of polymer and the conditions of treatment.

Any conjugated diene homopolymer or copolymer of a conjugated diene with a monomer containing a vinylidene(CH.sub.2 =C) group can be treated according to this invention. Conjugated dienes include butadiene-1,3; isoprene; 2,3-dimethylbutadiene-1,3; and the like. Monomers which can be used as comonomers with the conjugated dienes include styrene, vinyl-naphthalenes, vinylpyridines, and alkyl-substituted derivatives of these monomers as well as acrylonitrile, methacrylonitrile, methyl acrylate, methyl methacrylate, and the like. It is preferred that the hydrocarbon solution of the polymer be employed for the treatment. The polymer can be dissolved in a diluent such as a hydrocarbon or, in instances where the polymer is prepared in a diluent in the presence of an organometallic catalyst such as butyllithium, the treating agent can be added to the unquenched or quenched polymerization mixture. The treating temperature can be the same or used for the polymerization or it can be adjusted to some other level as desired. The preferred treating temperature is generally in the range of 50.degree. to 250.degree. F. The treating time is dependent upon the temperature and the result desired and can range from 1 minute or less to 100 hours or more. For most purposes the treating time is less than 25 hours and in many instances the desired results are obtained in less than 5 hours.

Any homogeneous olefin disproportionation catalyst can be employed for treating conjugated diene polymers according to this invention. Component (a) of the homogeneous olefin disproportionation catalyst which are typical of the present invention can be represented by the formula [(L).sub.a (L').sub.b M.sub.c Z.sub.d ] wherein (L) and (L') are organic or inorganic ligands; M is a transition metal of Group IB, IIIB, IVB, VB, VIB, or VIIB or the iron and cobalt subgroups of Group VIII; Z is halide or a radical such as CN, SCN, OCN, and SnCl.sub.3 ; a and d are numbers 0-6, b is 1-2, c is 1-4; x is a number indicative of the polymeric state of the compound; and wherein the number of (L), (L') and Z groups present in the component (a) compound shall not be greater than the number required for the metal to achieve the closed shell electronic configuration of the next higher atomic number inert gas and there must be at least one of L, L' or Z; preferred (L) groups are R.sub.3 Q, R.sub.3 QO, R.sub.2 Q--QR.sub.2, R.sub.2 NR', O, CO, R.sub.2 N--R.sup.2 --NR.sub.2, R-S-R, R.sup.3 S, [.pi.-(CHR.sup.4 --CR.sup.4 --CH.sub.2)], R.sup.5 (CN).sub.k, R.sup.5 (COO).sub.k, RCOR.sup.6 (COO).sub.k, [(RCO).sub.2 CH], (R.sub.2 NCSS) unsubstituted and R.sup.5 group-substituted pyridine, unsubstituted and R.sup.5 group-substituted bipyridine, or unsubstituted and R group-substituted cyclopentadienyl radicals; (L') ligands are NO, or [.pi.-(CHR.sup.4 --CR.sup.4 --CH.sub.2)] wherein R is an aromatic or saturated aliphatic radical, including radicals substituted with groups such as halo groups or alkoxy groups and the like, having up to 20 carbon atoms; R' is hydrogen or an R radical; R.sup.2 is a divalent R radical; R.sup.3 is a divalent saturated aliphatic or ethylenically unsaturated aliphatic radical having from 4 to 10 carbon atoms; R.sup.4 is hydrogen or methyl radical; R.sup.5 is an aromatic, saturated aliphatic, or ethylenically unsaturated aliphatic radical having up to 30 carbon atoms; R.sup.6 is a divalent saturated aliphatic radical having from 1 to 10 carbon atoms; Q is phosphorus, arsenic, or antimony; and k is 1-2.

The preferred component (a) compounds are complex compounds of the metals of Groups VIB, VIIB, and the iron and cobalt subgroups of Group VIII. The more preferred metals of these are molybdenum, tungsten, rhenium, ruthenium, or rhodium with the most preferred metal complex being a complex of molybdenum, such as NO-treated molybdenum trichloride disterate. Accordingly, the most preferred L' ligand is NO, and the most preferred L ligand correspond to the formula R.sup.5 (COO).sub.k.

In many instances the suitable (a) component need not be an isolated complex compound but can, for convenience and economy, simply be the admixture of a suitable, relatively simple, compound of a transition metal and one or more complexing agents. Thus, under complex-forming conditions, the admixture of these ingredients, complete with the diluent which is generally used to facilitate the mixing, can frequently be utilized without additional separation, isolation, or other treatment. For example, a suitable (a) component can be the admixture obtained by bubbling NO through a cyclohexane solution of molybdenum trichloride distearate.

The transition metal compounds which are applicable for use as the (a) component of the catalyst system of the present invention are generally compounds which are available or which can be prepared by methods which are conventional in the art.

When it is desired to prepare and utilize transition metal complex compounds in the form of nonisolated admixtures of its components, a transition metal compound and one or more complexing agents are merely combined in proportions and under conditions of temperature and time which permit the catalytically active transition metal complex to be formed, generally in a diluent in which the components are at least partly soluble. Suitable transition metal starting compounds, for example, are halides, oxyhalides, carbonyls, carbonyl halides, or salts of inorganic or organic acids, preferably halides.

Some specific examples of suitable transition metal complex (a) components are: (triphenylphosphine).sub.2 (NO).sub.2 MoCl.sub.2, (NO).sub.2 MoCl.sub.2, (pyridine).sub.2 -(NO).sub.2 MoCl.sub.2, NO-treated (triphenylphosphine).sub.2 MoCl.sub.4, NO-treated (pyridine).sub.2 MoCl.sub.4, NO-treated (butyronitrile).sub.2 MoCl.sub.4, NO-treated (stearate).sub.2 MoCl.sub.3, NO-treated pyridine-treated MoCl.sub.5, NO-treated (benzoate).sub.2 MoCl.sub.3, NO-treated (acetylacetonate).sub.2 MoO.sub.2, NO-treated MoOCl.sub.3, NO-treated tetrallyltin-treated MoCl.sub.5, No-treated MoCl.sub.5, NOCl-treated pyridine-treated MoO.sub.2, NO-treated tributylphosphine-treated MoCl.sub.5, NO-treated thiophene-treated MoCl.sub.5, NO-treated pyridine-treated WCl.sub.6, NO-treated benzoic acid-treated WCl.sub.6, (triphenylphosphine).sub.2 (NO).sub.2 WCl.sub.2, (triphenylphosphine).sub.2 ReOCl.sub.3, (triphenylphosphine).sub.2 ReCl.sub.4, (triphenylphosphine).sub.2 ReOBr.sub.3, (acetylacetonate).sub.4 Re.sub.2 Cl.sub.4, (triphenylphosphine)-ReOBr.sub.3, CO-treated triphenylphosphine-treated RuCl.sub.3, NO-treated RuCl.sub.3, NO-treated RuCl.sub.3, (triphenylphosphine).sub.4 (CO).sub.2 Ru.sub.2 (SnCl.sub.3)Cl.sub.3, NO-treated triphenylphosphine-treated RuCl.sub.3, NOCl-treated (triphenylphosphine).sub.3 RhCl, NO-treated (triphenylphosphine).sub.3 RhCl, (.pi.-allyl).sub.2 RhCl, NO-treated triphenylphosphine-treated RhCl.sub.3, (triphenylphosphine).sub.3 Cu.sub.2 Cl.sub.2, (triphenylphosphine)AuCl, [(triphenylphosphine)AgBr].sub.x, (triphenylphosphine)Cr(CO).sub.4, (triphenylphosphine).sub.2 MoCl.sub.4, SmCl.sub.3, ThCl.sub.4, UCl.sub.3, UCl.sub.4, (cyclopentadienyl)TiCl.sub.3, pyridine-treated TiCl.sub.4, (acetylacetonate).sub.4 Zr, NO-treated benzoic acid-treated NbCl.sub.5, NO-treated (triphenylphosphine).sub.2 CoCl.sub.2, NO-treated triphenylphosphine-treated IrCl.sub.3 and NO-treated CO-treated triphenylphosphine-treated IrCl.sub.3, and the like, and mixtures thereof.

The elements referred to herein are in accordance with the Periodic Table of Elements appearing in Handbook of Chemistry and Physics, Chemical Rubber Company, 45th edition (1964), page B-2.

The formula [(L).sub.a (L').sub.b M.sub.c Z.sub.d ].sub.x is used herein to identify the product obtained by the admixture, under catalyst forming conditions, of the metal compound with one or more ligand-forming materials whether or not the components are present in the complex as indicated in the formula.

When the (a) component of the catalyst is the product obtained by combining a compound of a transition metal, as hereinbefore discussed, with one or more suitable ligand-forming materials, these materials are simply combined under conditions of time and temperature which permit the complex to be formed. In general, excessively high temperatures at which the reagents tend to decompose, or excessively low temperatures, at which the reagents tend to crystallize or otherwise tend to become unreactive, should be avoided. The molar proportion of transition metal salt to the selected ligand-former can be in the range of from about 0.1:1 to about 10:1, preferably from about 0.2:1 to about 2:1. The products are obtained by combining these ingredients at a temperature preferably in the range of from about 0.degree. to about 130.degree. C., more preferably 20.degree. to about 60.degree. C., for a time in the range of from a few seconds up to about 24 hours, preferably in the presence of a diluent in which the components of the admixture are at least partially soluble. Any convenient diluent such as carbon tetrachloride, methylene chloride, xylene, cyclohexane, isooctane, benzene, chlorobenzene, and the like, can be used for this purpose. Any order of addition can be used. Such product need not be isolated but the mixture can be used directly in the formation of the catalyst system. In general, the (a) component of the catalyst system is fully prepared before contact is made with the (b) component.

The (b) component is an aluminum-containing compound, (1) represented by the formula RAlX.sub.2 ; (2) a mixture of (1) and a compound represented by the formula R.sub.n AlX.sub.m wherein R is as previously described, X is halogen, n is 2 or 3, m is 0 or 1, and the sum of n and m is 3; or (3) a compound represented by the formula R.sub.n AlX.sub.m which is as defined above.

Some specific examples of RAlX.sub.2 compounds are: methylaluminum dichloride, ethylaluminum dichloride, n-butylaluminum dichloride, n-heptylaluminum dibromide, cyclohexylaluminum dibromide, 4-methylcyclohexylaluminum difluoride, n-eicosylaluminum difluoride, isopropylaluminum diiodide, benzylaluminum dichloride, 2,4,6-trimethylphenylaluminum dichloride, n-decylaluminum dichloride and 2-naphthylaluminum.

Some non-limiting examples of (2) above are mixtures of a compound having the formula RAlX.sub.2 and a compound having the formula R.sub.2 AlX. Preferably, the mixture contains at least 50 mole percent of the former compound, although mixtures containing less than 50 mole percent can be used. The equimolar mixtures of those compounds are commonly called sesquihalides, and some specific examples of these compounds include methylaluminum sesquichloride, ethylaluminum sesquichloride, and ethylaluminum sesquibromide.

Some specific examples of R.sub.n AlX.sub.m compounds are; trimethylaluminum, triethylaluminum, tri-n-propylaluminum, triisobutylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum, tricyclohexylaluminum, triphenylaluminum, tri-n-decylaluminum, tri-n-eicosylaluminum, methyldiphenylaluminum, tribenzylaluminum, tri-l-naphtylaluminum, di-n-octylphenylaluminum, tri-4-tolylaluminum, dimethylaluminum chloride, di-n-propylaluminum bromide, diethylaluminum chloride, diisobutylaluminum chloride, methylisobutylaluminum chloride, di-n-heptylaluminum fluroide, dipheylaluminum bromide, dibenzylaluminum chloride and di-n-octylaluminum iodide.

The molar proportion of the (b) component to the (a) component to form the catalyst system of the present invention will generally be in the range of from about 0.1:1 to 20:1, preferably from about 1:1 to about 10:1.

Reaction temperature is not particularly important; however extremely high temperatures at which decomposition of the product or the catalyst might occur should be avoided and likewise extremely low temperatures at which reaction rates would be undesirably low should also be avoided. The reaction temperature will usually be the same temperature as that utilized in polymerizing the monomers or comonomers.

The following specific embodiments of the invention will be helpful in attaining a better understanding of the invention but the specific embodiments should be considered as exemplary and not as unduly limiting the invention.

The molybdenum trichloride distearate employed was prepared by reacting stearic acid with molybdenum pentachloride in cyclohexane. The recipe was as follows:

The materials were charged to the reactor which was then purged with nitrogen for 10 minutes. The temperature was adjusted to 122.degree. F. and maintained at that level for 15 hours. The reactor was then vented and purged with nitrogen for 15 minutes. The molybdenum trichloride distearate was soluble in cyclohexane. The calculated molarity of the solution was 0.36. A vessel containing the molybdenum trichloride distearate was pressured to 30 psig with NO for approximately 1 hour at room temperature (about 75.degree. F.) to obtain the reaction product used as one of the components in the catalyst system. This material was mixed with a cyclohexane solution of ethylaluminum sesquichloride in a ratio such that the gram atoms of Al to gram atoms of Mo was 5:1. This mixture was employed for treating polybutadiene.

Runs were conducted according to the invention in which butadiene was polymerized in the presence of n-butyllithium as the catalyst, and the unquenched reaction mixture was treated with the disproportionation catalyst formed on mixing the cyclohexane solution of ethylaluminum sesquichloride and the product obtained by reacting nitric oxide with molybdenum trichloride distearate as set forth above. The polymerization recipe was as follows:

Cyclohexane was charged to the reactor first after which it was purged with nitrogen. Butadiene was added and then the butyllithium. After a three-hour polymerization period, one run was reserved as a control. It was shortstopped with a 10 weight per cent solution of 2,2'-methylene-bis(4-methyl-6-tert-butylphenol) in a mixture of equal parts by volume of isopropyl alcohol and toluene. The amount of this solution used was sufficient to provide about one part by weight of the antioxidant per 100 parts by weight of the polymer. Variable quantities of the mixture of ethylaluminum sesquichloride and the reaction product of nitric oxide with molybdenum trichloride distearate (5:1 ratio of gram atoms Al:Mo) were added to the other runs and the temperature was maintained at 158.degree. F. for variable periods. Following the treating period, each reaction was shortstopped according to the procedure used in the control run. All polymers were recovered by coagulation in isopropyl alcohol. They were separated and dried. Cold flow, inherent viscosity, and Mooney values were determined. All polymers were gel free. Results were as follows:

These data show that treatment of the polymer with the disproportionation catalyst reduced cold flow, increased Mooney value, and increased inherent viscosity without producing gel.

A polyisoprene was prepared according to the recipe shown below and then treated with an MoCl.sub.3 (octanoate).sub.2 -(NO treated)/(CH.sub.3 CH.sub.2) Al.sub.2 Cl.sub.3 (EASC) catalyst.

Charge order: cyclohexane, nitrogen purge, isoprene, n-butyllithium.

Polyisoprene (40 g), prepared as described, was treated (in the absence of a separate termination or "shortstopping" step and polymer isolation) with EASC/MoCl.sub.3 (octanoate).sub.2 .sub.[(NO treated) as indicated below in Table II.

b. Prepared by refluxing a mixture of cyclohexane (76.7 g.), octanoic acid (103.8) and molybdenum pentachloride (100 g) for 1.17 hours under nitrogen. This soluble product was 0.315 M in MoCl.sub.3 (octanoate).sub.2. A portion of this solution was transferred to another vessel and pressured repeatedly with NO while being shaken until the pressure no longer decreased on standing at room temperature. This solution was diluted to 0.032 M in molybdenum content with cyclohexane.

c. Inherent viscosity. Polymers were gel free.

d. ML-4 at 212.degree. F.

e. g atom/hm = milligram atoms per 100 g of monomers.

f. In this run, the EASC was added to the polyisoprene solution first and this mixture agitated at 70.degree. C. for 0.25 hours. The MoCl.sub.3 (octanoate).sub.2 -(NO treated) was then added and the mixture agitated at 70.degree. C. for 1 hour.

This example demonstrates that the process of the invention is applicable to conjugated diene homopolymers such as polyisoprene.

A butadiene/styrene block polymer was prepared employing the recipe shown below.

Charge Order: cyclohexane, nitrogen purge, styrene, butadiene, n-butyllithium.

A butadiene/styrene block copolymer (40 g), prepared as described, was treated as described above for polyisoprene. The results obtained are given in Table III.

This example demonstrates that the invention is applicable to conjugated diene copolymers such as a butadiene/styrene block copolymer.

A series of runs were conducted in which polybutadienes were prepared according to the recipe shown below and then treated with the MoCl.sub.3 (octanoate).sub.3 -(NO treated)/EASC using varying Al/Mo mole ratios.

Charge Order: cyclohexane, nitrogen purge, butadiene, n-butyllithium.

Polybutadienes (40 g each), prepared as described above, were treated in the same manner as described above for polyisoprene. The results obtained in these runs are given in Table IV below.

a. All polymers were gel free.

This example demonstrates that the process of the invention is applicable to conjugated diene homopolymers such as polybutadienes using a wide range of Al/Mo mol ratios.

In each of the runs of Examples II-IV, after treatment the polymers were recovered by the following procedure. Each reaction mixture (containing a 40 g monomer charge) was terminated at the end of the treatment period by the addition of about 50 ml of an 80/20 by volume mixture of toluene/isopropyl alcohol. The resulting mixture was thoroughly mixed and then charged with 10 ml of a solution of an antioxidant, 2,2'-methylene-bis(4-methyl-6-tert-butyphenol), in isopropyl alcohol (0.1 g/ml). This mixture was also mixed thoroughly and then the polymer in each mixture was recovered by coagulation with isopropyl alcohol. Each polymer was separated and then dried under vacuum at 145.degree. F. In each run, the weight of the recovered polymer was essentially 100 percent of the weight of the monomers charged.

A polybutadiene having at least 85% cis-1,4 addition was prepared according to the recipe shown below and treated with the following catalysts: (A) MoCl.sub.3 (octanoate).sub.2 -(NO treated)/(CH.sub.3 CH.sub.2) Al.sub.2 Cl.sub.3 and (B) MoCl.sub.3 (octanoate).sub.2 -(NO treated)/(i-C.sub.4 H.sub.7).sub.3 Al.

Charge Order: toluene, 1,3-butadiene, iodine solution, cool to 5.degree. C., triisobutylaluminum and titanium tetrachloride.

The reactor effluent containing the stereospecific polybutadiene was treated (in the absence of a separate termination or "shortstopping" step and polymer isolation) with catalyst (A) and (B) according to the following recipe:

The results of the treatment are summarized in the following Table V:

The treated cis-polybutadiene polymers were recovered by adding to each reaction mixture about 1 phr (parts per one hundred parts polymer) of antioxidant, 2,6-di-tert-butyl-4-methylphenol, added as a 10 weight percent solution of the antioxidant in a 50/50 by volume mixture of isopropyl alcohol and cyclohexane, and the mixture coagulated with isopropyl alcohol. The polymer from each mixture was separated and dried under vacuum.

The above Table V demonstrates that the properties of a butadiene polymer containing high amounts of cis-1,4 addition can be modified in accordance with the invention. Although not completely understood, it is believed that Runs 5, 11 and 12 did not increase cold flow due to the participation of residual butadiene monomer in the treatment step.

A polybutadiene polymer was prepared using an organolithium catalyst system according to the following recipe:

Charge Order: cyclohexane, 1,3-butadiene, n-butyllithium.

The reaction mixture was shortstopped with isopropyl alcohol and the reaction mixture diluent was evaporated. The polymer residue from the evaporation was dried under vacuum.

The dried polymer was redissolved in cyclohexane and treated with a NO-treated molybdenum trichloride dioctanoate/ethylaluminum sesquichloride catalyst system. The treatment recipe and results are summarized in Table VI.

The treated polymer was recovered in the same manner as described above in Example V.

This example demonstrates that the process of the invention is applicable to terminated and redissolved polymers of butadiene as well as polymers of butadiene which have not been quenched and separated from the polymerization diluent.

Reasonable variation or modification of the invention is possible without departing from spirit or scope thereof.