Diester of 3,5,3',5'-Tetrabromo-Bisphenol a With Halogenated Aromatic Carboxylic Acid

This invention relates to novel bromine containing diester compounds which are particularly useful for imparting flame-retardancy to various polymeric materials.

A typical example of bromine containing flame-retardant additives known in the art is deca-bromodiphenyl-ether. This compound, however, is very inferior in weathering resistance. As another example, there is also known 3,5,3',5'-tetrabromo-bisphenol A, which will disadvantageously lower heat distortion temperature of polymeric materials to a great extent when incorporated therein.

British Pat. No. 1,281,937 discloses a compound of the formula: ##STR3## wherein R is an alkyl group having 1 to 3 carbon atoms. This compound also has the drawback to lower remarkably heat distortion temperature of polymeric materials to which said compound is added.

U.S. Pat. No. 3,846,469 discloses a compound of the formula: ##STR4## wherein m is integer of 3 to 5. Such a compound can be added to polymeric materials for improvement of flame-retardancy only with disadvantageous decrease in impact strength of polymeric materials.

Furthermore, there is reported a compound of the formula: ##STR5## wherein n is 1 or 2, in Journal of Chemical and Engineering Data, Vol. 12, p. 252(1967). The compound is by far inferior in the effect of imparting flame-retardancy to polymeric materials to the compound of the present invention. Accordingly, in order to obtain equal levels of improvement in flame-retardancy, it is required to add a large amount of such a compound of inflammable polymeric materials, whereby other properties such as weathering resistance, heat distortion temperature and impact strength, etc. of the resultant polymeric materials are greatly impaired.

In accordance with the present invention, there is provided a novel diester compound represented by the following formula (I): ##STR6## wherein R.sub.1 and R.sub.2, which may either be identical or different, represent the groups of the formula (II): ##STR7## wherein n is an integer of 0 to 4; and m an integer of 1 to 5.

Typical examples of R.sub.1 and R.sub.2 may include 2-bromophenyl; 3-bromophenyl; 4-bromophenyl; 2,6-dibromophenyl; 2,3-dibromophenyl; 2,4-dibromophenyl; 2,5-dibromophenyl; 3,4-dibromophenyl; 3,5-dibromophenyl; 2,4,6-tribromophenyl; 2,3,4,5-tetrabromophenyl; 2,3,5,6-tetrabromophenyl; 2,3,4,5,6-pentabromophenyl; 2,4,6-tribromophenylmethyl; 2,4,6-tribromophenylethyl; 2,4,6-tribromophenylpropyl; 2,4,6-tribromophenylbutyl; and the like.

The compound of the present invention has excellent heat stability and weathering resistance as well as excellent effect of imparting flame-retardancy to inflammable polymeric materials, and is also free from the drawbacks of lowering impact strength and heat distortion temperature of polymeric materials when incorporated therein.

The compound of the present invention can be prepared according to various methods. For example, according to one method, it can be prepared by esterification of 3,5,3',5'-tetrabromo-bisphenol A with one or two carboxylic acid having the groups (II) as mentioned above, which may be the same or different, in a non-alcoholic solvent such as benzene, toluene, tetrahydrofuran, ether or pyridine, using an acid catalyst such as sulfuric acid, hydrogen chloride, an aromatic sulfonic acid derivative, p-toluenesulfonic acid, phosphorus oxychloride, polyphosphoric acid, boron trifluoride, phosphorus pentachloride, boric acid-sulfuric acid, boron trifluoride etherate, trifluoroacetic acid, dicyclohexyl carbodiimide, etc.

As an alternative method, a carboxylic acid having the groups as represented by the formula (II) can be first converted to an acid halide by reaction with a reagent such as phosphorus trichloride, phosphorus pentachloride, thionyl chloride, triphenylphosphine dibromide, triphenylphosphine-carbon tetrachloride, thionyl chloride-dimethylformamide, thionyl chloride-pyridine (in the presence of zinc chloride catalyst), thionyl chloride-iodine, phosphorus pentachloride-acetyl chloride, etc. in the absence of a solvent or in a solvent such as benzene, methylene chloride, chloroform, tetrahydrofuran, ether, etc. The resultant acid halide is then subjected to esterification with 3,5,3',5'-tetrabromo-bisphenol A in the presence of a base such as sodium hydroxide, potassium hydroxide, dimethyl aniline, pyridine, sodium hydride, tetramethyl urea, and the like.

According to another method, a carboxylic acid anhydride having the groups as represented by the formula (II) can be esterified with 3,5,3',5'-tetrabromo-bisphenol A in the presence of a catalyst selected from sulfuric acid, zinc chloride, chlorosulfonic acid, sodium acetate, sodium methylate, p-toluenesulfonic acid and pyridine.

Furthermore, there may also be employed a method in which a nitrile having the groups of the formula (II) is reacted with 3,5,3',5'-tetrabromo-bisphenol A under anhydrous conditions in the presence of an acid catalyst such as hydrogen chloride, hydrogen bromide, hydrogen iodide, sulfuric acid, p-toluenesulfonic acid, etc.

The polymeric materials to which flame-retardancy can be imparted by the compound according to the present invention may be exemplified by polystyrene (including rubber-modified high impact polystyrene), AS resin, ABS resin, polyphenylene oxide, polyester, polyamide, polyethylene, polypropylene, polyisoprene, polybutadiene, polyacrylate, polycarbonate, etc. Polymeric mixtures comprising two or more of these polymers in suitable blending ratios may also be available.

If desired, other halo-containing flame-retardants and/or phosphorus-containing flame-retardants may also be used in combination with the compound of the present invention. Furthermore, there may also be added one or more synergetic flame-retardants such as antimony trioxide, zirconium silicate, zinc borate, titanium phosphate, red phosphorus, molybdenum oxide and others.

The effective amount of the present compound to be added for imparting flame-retardancy may depend on the extent of flame-retardancy required and the polymeric material to be applied. For example, for a polystyrene to be acceptable as V-O rate according to the UL-94 test method, it is necessary to add 10 to 30 parts by weight of the compound of the present invention and 2 to 10 parts by weight of antimony trioxide per 100 parts by weight of polystyrene. For all of the resins as mentioned above, preferable compositions comprise 100 parts by weight of an inflammable polymer, 5 to 40 parts by weight of a compound of the present invention and 0 to 15 parts by weight of antimony trioxide. Furthermore, there may also be added other conventional additives together with the compound of the present invention, such as stabilizers, coloring agents, anti-static agents, foaming agents, light stabilizers, fillers, etc.

The present invention is explained in further detail with reference to the following Examples, by which the present invention is not limited but various modifications are possible within the spirit of the invention.

In a flask equipped with a reflux condenser, 84 g (0.3 mole) of 3,5-dibromobenzoic acid and 68 g (0.33 mole) of phosphorus pentachloride were reacted under reflux for one hour. After removal of phosphorus oxychloride under reduced pressure by means of an aspirator, the reaction product was subjected to vacuum distillation under 8 mm Hg to obtain 63 g of 3,5-dibromobenzoic acid chloride, melting at 125.degree. to 130.degree. C.; in the form of a colorless transparent liquid (yield: 70%).

While stirring a solution of 54.4 g (0.1 mole) of 3,5,3',5'-tetrabromo-bisphenol A and 30 ml of pyridine in 300 ml of tetrahydrofuran at room temperature, 60 g (0.2 mole) of the above 3,5-dibromobenzoic acid chloride was slowly added dropwise, whereby white crystals were formed immediately. After the dropwise addition, stirring was continued for additional three hours at room temperature to complete the reaction, followed by evaporation of tetrahydrofuran. The residual crystals were dissolved in chloroform and the resultant solution was washed twice with ammonia water and three times with water. Thereafter, the washed solution was dried over anhydrous sodium sulfate, followed by removal of the solvent. The resultant crystals were recrystallized from ethanol/benzene (1:4) to give 96 g of white crystals (yield: 90%, m.p.: 271.degree. C.).

Elemental analysis: C.sub.29 H.sub.16 Br.sub.8 O.sub.4 -- Calculated: C, 32.58; H, 1.50; Br, 59.93; Found: C, 32.67; H, 1.43; Br, 59.40.

Infra-red spectrum: Absorptions of ester found at 1760 cm.sup.-1 and 1240 cm.sup.-1.

According to the same procedure as in Example 1 except that 60 g (0.3 mole) of p-bromobenzoic acid was used in place of 3,5-dibromobenzoic acid, the reaction was carried out to obtain 86 g of white crystals of di-(4-bromobenzoic acid)ester (yield: 95%, m.p.: 225.degree. C.).

Elemental analysis: C.sub.29 H.sub.18 Br.sub.6 O.sub.4 -- Calculated: C, 38.24; H, 1.98; Br, 52.75; Found: c, 38.31; H, 1.95; Br, 52.46.

Into a four-necked flask equipped with a reflux condenser, there were charged 54.4 g (0.1 mole) of 3,5,3',5'-tetrabromo-bisphenol A and 28 g (0.1 mole) of 3,5-dibromobenzoic acid and then 300 ml of tetrahydrofuran was added thereto. The mixture was stirred until completely dissolved and to the resultant solution was added slowly 63 g (0.3 mole) of trifluoroacetic acid anhydride under stirring. After completion of the addition, stirring was continued for additional one hour. Then, a solution of 20.1 g (0.1 mole) of p-bromobenzoic acid in 70 ml of tetrahydrofuran was slowly added to the reaction mixture, whereby white crystals were precipitated. After completion of the dropwise addition, stirring was continued for additional one hour and thereafter tetrahydrofuran and excessive trifluoroacetic acid anhydride were removed by evaporator. The resultant crystals were dissolved in chloroform, washed with an aqueous sodium hydrogen carbonate solution and dried over anhydrous sodium sulfate, followed by removal of the solvent, to give 94 g of white powders (yield: 95%).

Elemental analysis: C.sub.29 H.sub.17 O.sub.4 Br.sub.7 -- Calculated: C, 35.19; H, 1.72; Br, 56.62; Found: C, 35.23; H, 1.71; Br, 56.58.

Infra-red spectrum: Absorptions of ester found at 1760 cm.sup.-1 and 1240 cm.sup.-1.

A mixture comprising 100 parts by weight of a high impact polystyrene (Styron 475D, trade mark, produced by Asahi-Dow Limited, Japan), 20 parts by weight of the di-(3,5-dibromobenzoic acid)ester as prepared in Example 1 and 5 parts by weight of antimony trioxide was prepared in a drum blender and extruded at 250.degree. C. into pellets by an extruder having a Dulmage type screw. Using an injection molding machine, these pellets were molded at 220.degree. C. into test pieces with thickness of 1/8". There was substantially no discoloration of the resin in the test piece even by molding after permitting the resin to be molded to reside in the cylinder of the molding machine for 10 minutes, indicating good heat stability. When burning test was conducted according to the test method UL-94, the test samples were found to be self-extinguishing with V-O rate. The test samples were also found to have an Izod impact strength with notch of 7.5 Kg.cm/cm (according to JIS-K6871), which impact strength was retained at as high as 6.0 Kg.cm/cm when measured after irradiation of the sample by Sunshine Weather-meter for 400 hours. The sample was also found to have a Vicat softening point (ASTM-D 1525) of 103.degree. C.

One hundred parts by weight of a polyphenyleneoxide resin (Xyron 500 H: produced by Asahi-Dow Limited), 20 parts by weight of the di-(3,5-dibromobenzoic acid)ester as prepared in Example 1 and 5 parts by weight of antimony trioxide were blended in a blender and extruded at 250.degree. C. into pellets by an extruder having a Dulmage type screw. Then, the pellets were injection molded into test pieces with thickness of 1/8". Burning test was conducted according to the test method UL-94, whereby the samples were found to be self-extinguishing with V-O rate.

A mixture comprising 100 parts by weight of a polybutylene terephthalate resin (PBT 1401 of a Toray's product), 20 parts by weight of the di-(3,5-dibromobenzoic acid)ester as prepared in Example 1 and 7 parts by weight of antimony trioxide was prepared in a drum blender and extruded at 250.degree. C. into pellets by an extruder having a Dulmage type screw. Then, the pellets were injection molded into test pieces with thickness of 1/8". Burning test was conducted according to the test method UL-94, whereby the samples were found to be self-extinguishing with V-O rate.

The same procedure as in Example 6 was repeated except that 100 parts by weight of nylon 6 (Toray's Amilan 1017) were used in place of the polybutylene terephthalate resin and that the amount of the di-(3,5-dibromobenzoic acid was changed to 15 parts by weight. The result of the burning test was the same as in Example 6.

Flame-retardant polystyrene compositions were prepared according to the same procedure as in Example 4 except for using different diesters as prepared in Examples 2 and 3 for the compositions of Examples 8 and 9, respectively. The result of burning test conducted by the same method as in Example 4 for any of the samples prepared from these compositions was similar to that as reported in Example 4.