Document mpDgaR9zq5LQR156QbX32Vo8k

United States Patent [19] Kochi et al. [ii] Patent Number: 4,857,576 [45] Date of Patent: Aug. 15,1989 [54] METHOD FOR RENDERING A FLAMMABLE POLYMER MATERIAL FLAME-RESISTANT [75] Inventors: Hiromi Kochi; Kenji Fukunaga, both of Fukuyama; Takaharu Itagaki, Yokohama; Tsuyoshi Ito, Machida, all of Japan [73] Assignees: Mitsubishi Kasei Corporation, Tokyo; MANAC Incorporated, Fukuyama, both of Japan [21] Appl. No.: 843,914 [22] Filed: Mar. 21,1986 Related U.S. Application Data [63] Continuation of Ser. No. 646,079, Aug. 31, 1984, aban doned. [30] Foreign Application Priority Data Sep. 20, 1983 [JP] Japan .................................. 58-173656 [51] IntCL4 C08K 3/22 [52] U.S. Q..................................... 524/409; 525/151; 525/165; 525/184; 525/214; 525/223; 525/235; 525/240; 525/241; 525/327.1; 525/329.5; 525/332.2 [58] Field of Search................. 525/165, 332.2, 329.5, 525/327.1, 151, 184, 214, 223, 235, 240, 241, 165; 524/409 [56] References Cited U.S. PATENT DOCUMENTS 3,474,067 10/1969 Praetzel et al......................... 525/214 4,246,354 1/1981 Herbin et al........................ 525/332.2 4,352,909 10/1982 Barda et al............................. 525/157 Primary Examiner--Jacob Ziegler Attorney, Agent, or Firm--Obion, Spivak, McClelland, Maier & Neustadt [57] ABSTRACT A method for rendering a flammable polymer material flame-resistant, which comprises incorporating to the flammable polymer material a powder of a cross-linked aromatic polymer brominated to contain from 30 to 70% by weight of bromine. 16 Claims, No Drawings PLAINTIFF'S EXHIBIT 0 4,857,576 12 wherein a linear polystyrene is brominated under a METHOD FOR RENDERING A FLAMMABLE specific condition. It is disclosed that the brominated POLYMER MATERIAL FLAME-RESISTANT polystyrene thereby obtained is incorporated to other plastics as a flame retardant. Furthermore, in U.S. Pat. This application is a continuation of application Ser. 5 No. 3,474,067, it is disclosed that a nuclear-brominated No. 646,079, filed Aug. 31, 1984, now abandoned. polystyrene is obtained by the polymerization of appro BACKGROUND OF THE INVENTION priate nuclear-brominated styrene, and it is incorpo rated to a polyolefin to obtain a flame retarded composi 1. Field of the Invention tion. By using these high molecular weight flame retar The present invention relates to a method for impart 10 dants, the blooming may be prevented to some extent. ing flame retardancy to a flammable polymer material However, as shown by the Comparative Examples such as a plastic or a rubber by incorporating a specific given hereinafter, they are not yet fully satisfactory. flame retardant therein. More particularly, the present Also from the viewpoint of the handling of organic invention relates to such a method wherein a bromi- halogen flame retardants, high molecular weight flame nated cross-linked aromatic polymer is used as the flame 15 retardants are considered more advantageous than low retardant. molecular weight flame retardants in view of the safety 2. DESCRIPTION OF THE PRIOR ART including the working environment. However, the Flammable polymer materials such as plastics or rub above-mentioned conventional flame retaedants are bers have various excellent characteristics such as their soluble in organic solvents, and therefore are not ade processability, electric characteristics, mechanical 20 quately satisfactory from the viewpoint of environmen properties and stability. They have been used in a vari tal pollution. ety of applications in which such excellent characteris There is an increasing demand for flame retardancy tics are utilized. There have been remarkable develop of flammable polymer materials and such a trend be ments in such polymer materials. However, most of the comes stronger year after year. The selection of an polymer materials have a drawback that they are flam 25 organic halogen flame retardant has become important mable or combustible. for the flame retardancy including heat resistance. In their applications particularly for constructional materials and electronic parts, they are, in many cases, SUMMARY OF THE INVENTION subject to various legal restrictions concerning flame Under the circumstances, the present inventors have retardancy. 30 conducted extensive researches and have found that the As a method for imparting flame retardancy to flam above-mentioned drawbacks may be substantially re mable polymer materials such as plastics or rubbers, it duced by using a brominated cross-linked aromatic has been known to incorporate to the flammable poly copolymer having a three dimensional structure as a mer materials, organic halogen compounds such as flame retardant. The present invention is based on this hexabromobenzene, decabromobiphenyl ether and tet- 35 discovery. rabromobisphenol A; organic phosphorus compounds Namely, the present invention provides a method for such as dibromopropyl phosphate, tricresyl phosphate rendering a flammable polymer material flame-resistant, and cresyldiphenyl phosphate, and inorganic com which comprises incorporating into the flammable pol pounds such as antimony trioxide, alumina and calcium ymer material a powder of a cross-linked aromatic poly carbonate, alone or in combination. Among them, or 40 mer brominated to contain from 30 to 70% by weight of ganic halogen compounds have been widely used in bromine. many fields because they are particularly superior in the The flame retardant of the present invention is a flame retarding effect, and kinds of flame retardants are cross-linked copolymer and accordingly is not soluble increasing year after year. in any solvent. Thus no absorption into a living body However, among the most commonly used organic 45 takes place. Further, it does not melt by heat and has halogen retardants, typical additive-type flame retar excellent thermal stability. Furthermore, it is free from dants such as decabromobiphenyl ether, hexabromo blooming since it molecular weight is great. Thus, the benzene and tetrabromobisphenol A have not only a brominated cross-linked aromatic polymer of the pres problem of the heat stability of the flame retardants ent invention is a superior flame retardant. themselves when applied to e.g. saturated polyester 50 resins having relatively high molding temperature, but also a serious technical problem which has recently DETAILED DESCRIPTION OF THE INVENTION been raised and which is concerned with a blooming Now, the present invention will be described in detail phenomenon wherein a part of the flame retardant in with reference to the preferred embodiments. the molded resin tends to migrate to the surface of the 55 In the present invention, a powder of a brominated molded resin, whereby the commercial value of the cross-linked aromatic polymer containing from 30 to product will be seriously damaged. 70% by weight of bromine, is used as a flame retardant. Various technical studies have been made in recent Such a brominated cross-linked aromatic polymer is years to solve these problems. Among them, a proposal prepared by brominating a cross-linked aromatic co for increasing the molecular weight of the fire retardant 60 polymer. The cross-linked aromatic copolymer as the itself has been regarded as of particular interest as a starting material may be prepared.by the copolymeriza technical theme. For instance, a brominated epoxy tion of a monovinyl aromatic compound with a polyvi oligomer (Japanese Examined Patent Publication No. nyl compound, or by the cross linking of a linear polyvi 39264/1982), a brominated polycarbonate or a bromi nyl aromatic compound. nated polyphenylene has been proposed. Further, U.S 65 In the case of the preparation of the cross-linked Pat. No. 4,352,909 and DE No. 3,061,057 (Japanese aromatic copolymer by the compolymerization of the Unexamined Patent Publication No. 151007/1980) dis monovinyl compound with the polyvinyl compound, a close a process for preparing a brominated polystyrene. monovinyl aromatic monomer such as styrene, vinyltol- T y SJ i ym/ t \J 34 uene or vinylnaphthalene is useful as the monovinyl The bromination of the gel or porous copolymer thus compound. As the polyvinyl monomer, a polyvinyl obtained, is conducted by means of a brominating agent, aromatic monomer such as divinylbenzene, divinylxy- preferably at a temperature within a range of from 0 to lene or trivinylbenzene is most useful. However, a poly 100 C. As the brominating agent, a bromine-generating vinyl heterocyclic compound such as divinyl pyridine 5 agent such as sulfuryl bromide or molecular bromine or trivinyl pyridine, or a polyvinyl aliphatic monomer may be used. In the case where molecular bromine is such as ethylene glycol dimethacrylate or trimethylol used, a suitable bromination temperature is from 0 to propane trimethacrylate, is also useful. Further, for the 50 C., and such a bromination reaction is usually com purpose of improving the copolymerizability of the pleted in from 2 to 20 hours. The amount of bromine to monovinyl monomer with the polyvinyl monomer, it is 10 be introduced varies depending upon the amount of the possible to incorporate a polymerizable monomer such brominating agent or the reaction condition for the as acrylonitrile, methylmethacrylate, octadiene or iso- bromination. However, it is preferred to conduct the prene as a third component. The ratio of the polyvinyl bromination so that the bromine content in the resulting compound to the monovinyl compound may optionally brominated copolymer is from 30 to 70% by weight. It be varied. However, in order to facilitate the introduc- 15 is preferred to use a catalyst such as ferric chloride or tion of bromine in an adequate amount and to improve aluminum chloride to perform the bromination reaction the pulverization property of the resulting polymer, the smoothly. The amount of such a catalyst is preferably polyvinyl compound is usually used in an amount of within a range of from 0.025 to 0.2 g relative to 1 g of from 2 to 50% by weight, preferably from 3 to 20% by the copolymer. weight, based on the total vinyl compounds. In order to 20 Further, it is preferred that prior to the bromination facilitate the pulverization of the resulting copolymer, it is also possible to make the copolymer porous. A method of forming a porous structure is known. For reaction, the copolymer is preliminarily swelled by means of a swelling agent such as dichloroethane or dibromoethane. instance, as disclosed in the book "Ion Exchange ResinChelate Resin" (compiled by Yoshimasa Hojo and pub- 25 lished by Kodansha Scientific Co. in 1976) at page 129 et seq, it is common to employ a method wherein poly merization is conducted in the presence of a component After the completion of the bromination reaction, the brominated cross-linked copolymer thus obtained is washed with a sufficient amount of water and then with an organic solvent such as methanol or acetone, and which does not participate in the polymerization and then dried. Then, the polymer is pulverized to a particle which is incorporated as an additive in the monomer 30 size of from 0.1 to 10 /xm. For the pulverization, a con mixture. The amount of such an additive may be option ventional method may be employed. However, it is ally varied but is usually from 0 to 200% by weight preferred to use a pulverizer such as a hammer mill. based on the monomer mixture. The flame retardant of the present invention is usu The polymerization may be conducted by subjecting ally used in an amount of from 0.1 to 40 parts by weight, the monomer mixture to a conventional polymerization 35 preferably from 3 to 30 parts by weight, relative to 100 method. As a simple method, it is advantageous to em parts by weight of the flammable polymer material. If ploy a method of heating under a suspended state or the amount is less than 0.1 part by weight, no adequate bulk state in the presence of a polymerization initiator. flame retarding effect is obtainable. On the other hand, When the polymerization is conducted under a sus if the amount exceeds 40 parts by weight, the properties pended state, the amount of the polymerization initiator 40 of the polymer material such as impact resistance or is usually within a range of from 0.05 to 5.0% by weight transparency, tend to be impaired. based on the monomer mixture. As the polymerization As the flammable polymer material to be flame- initiator, there may be used a variety of polymerization retarded by the present invention, there may be men initiators. However, in general, a peroxide such as ben tioned a variety of flammable high molecular resins zoyl peroxide or lauroyl peroxide, or an azo-type poly- 45 such as a polyacetal, a polycarbonate, a polyamide, a merization initiator such as azobisisobutyronitrile, is polyphenylene oxide, a polysulfone, a polyarylate, a preferably used. When the polymerization is conducted polyphenylene sulfide, a polyethylene terephthalate, a under a suspended state, the monomer mixture is stirred polybutylene terephthalate, a polymethacrylate, a poly in water as a medium in the presence of a proper disper ethylene, a polypropylene, a polystyrene, an AS resin, sant, to carry out the polymerization. The polymeriza- 50 an ABS resin and a mixture thereof. tion differs depending upon the type of the polymeriza The flame retardant of the present invention may be tion initiator. In the case of benzoyl peroxide, the poly used alone to impart flame retardancy to the flammable merization is conducted at a temperature of from 60 to polymer. However, in order to obtain adequate effec 80 C. for from 8 to 20 hours under stirring. After the tiveness with a minimum amount, it is preferred to use it polymerization, the obtained copolymer is thoroughly 55 in combination with a flame retardant assistant. As such washed with water, and in the case where an additive is a flame retardant assistant, it is preferred to employ an incorporated, the additive is removed by an operation antimony compound such as antimony trioxide, anti such as extraction, and then the product is dried. mony pentoxide or antimony tartrate. Particularly pre A method for producing a cross-linked polymer by ferred is antimony trioxide. the cross linking of a linear polyvinyl compound, is also 60 The incorporation of the flame retardant of the pres known. For instance, as disclosed in Die Angewandte ent invention to the synthetic resin can be conducted by Makromolekulare chem No. 91, pages 127-142 (1980) a conventional mixing method. There may be men V. A. Davankov and M. P. Tsyurupa, it is useful to tioned a method of mixing and extruding by means of an employ a method wherein a linear polystyrene is cross- extruder, a method of simple mixing, followed by direct linked by Friedel-Crafts reaction. As the linear polyvi- 65 injection molding, or a method of adding the flame nyl compound, a polyvinyl aromatic polymer such as retardant during the preparation of the resin. Further, it polystyrene, polyvinyl toluene or poly-a-methyl sty may be incorporated together with a reinforcing agent rene, is useful. such as a glass fiber, a filler, a heat stabilizer, an antioxi 4,857,576 56 dant or a light stabilizer as well as an additive such as a ture for 8 hours. After the completion of the reaction, 3 plasticizer, a lubricant or a coloring agent. liters of water was added and the mixture was ade Now, the present invention will be described in fur quately stirred. Then, water was withdrawn, and the ther detail with reference to Examples. However, it dichloroethane solution was added to 20 liters of metha should be understood that the present invention is by no 5 nol. The precipitated polymer was collected by filtra means restricted by these specific Examples. In the tion, washed with 1 liter of methanol and then dried. Examples, the tensile strength was measured in accor The yield of the brominated polystyrene was 250 g. The dance with ASTM-D-638, and the flame retardancy bromine content was 66.1%. This polymer was soluble was measured in accordance with UL 94 test method. in a solvent such as dichloroethane, toluene, xylene or Bleeding was visually evaluated after a sample piece 10 dimethylformamide. was left in an oven at 60" C. for 72 hours and at 130 C. for 72 hours. Sample No. 1 Bromination of a cross-linked aromatic EXAMPLES 1 to 3 and COMPARATIVE EXAMPLES 1 to 5: Evaluation of flame retardancy copolymer The non-brominated cross-linked aromatic copoly Into a four-necked flask, 100 g of a porous polysty 15 mer used as the starting material for Sample No. 1, the rene cross-linked with 4% by weight of divinylbenzene brominated cross-linked aromatic (co)polymers of Sam was introduced, and 500 g of dichloroethane was added. ples Nos. 1 to 3, the brominated polystyrene of Sample The mixture was left to stand at room temperature for 1 No. 4, decabromobiphenyl ether and hexabromoben- hour, and then 5 g of ferric chloride and 434 g of molec zene were taken, and respectively pulverized by a sand ular bromine were added. The mixture was reacted at 20 grinder to an average size of at most 1 jam. room temperature for 8 hours. After the completion of Then, 80 g of each pulverized flame retardant was the reaction, 3 liters of water was added, and the mix incorporated to 1 kg of an aromatic polycarbonate resin ture was heated to 90* C., whereby dichloroethane was (Panlite K1300, manufactured by Taijin Limited), and azeotropically distilled off. Then, the copolymer was the mixture was kneaded by a laboratory Brabender at washed with water and further washed with 2 liters of 25 270" C. The blend was molded at 280" C. by a compres acetone, 3 liters of IN HC1 and 3 liters of desalted wa sion molding machine, and then the flame retardancy ter, and then dried at 80" C. for 8 hours. The yield of the was evaluated in accordance with UL-94 test method. brominated copolymer was 272 g, and the bromine The evaluation was made on the basis of four grades of content was 63.8% by weight. HB, V-2, V-l and V-0. The results are shown in Table Sample No. 2 30 1. The same treatment as in the preparation of Sample No. 1 was conducted except that 100 g of a porous polystyrene cross-linked with 10% by weight of divi nylbenzene was used as the cross-linked aromatic co polymer, whereby 233.0 g of a brominated copolymer 35 was obtained. The bromine content of this copolymer was 57.2%. The brominated copolymers i.e. Sample Nos. 1 and 2 were insoluble in most organic solvents. Com para tive Exam TABLE 1 Evaluation of the flame retardancy and blooming Blooming Flame retardant 60 C. for 130 C. for UL-94 72 hrs. 72 hrs. None HB No No Sample No. 3 Cross linking and bromination of a 40 ple l linear polymer 200 g of a poly-a-methylstyrene having a molecular Com para tive weight (weight average) of 10,000 was dissolved in 5 Exam Non-brominated copoly mer for Sample No. 1 HB No No liters of dichloroethane, and the solution was intro ple 2 duced in a 10 liter polymerization reactor equipped with a condenser. Then, 35 g of paraxylene dichloride 45 Exam ple l Exam and 52.2 g of stannic chloride were added, and the mix ple 2 Brominated copolymer of Sample No. I Brominated copolymer of Sample No. 2 V-0 V-0 No No No No ture was reacted at 80" C. for 16 hours. After the com Exam pletion of the reaction, the formed bulky cross-linked ple 3 polymer was collected by filtration, roughly pulverized 50 Com para to a size of from 1 to 2 mm. Then, it was washed succes tive Brominated copolymer of Sample No. 3 Brominated poly styrene of Sample No. 4 V-0 V-0 No No No Slightly yes sively with 2 liters of diochloroethane, 2 liters of metha Exam nol and 2 liters of water, and then dried at 80" C. for 8 hours. The yield of the obtained cross-linked polymer ple 3 Com para was 207 g. It was insoluble in a solvent such as dichloro 55 tive Decabromobiphenyl ether V-0 Yes Yes ethane, toluene, xylene, dimethylformamide or acetoni trile, which is capable of dissolving a poly-a-methylsty rene. 100 g of this cross-linked polymer was treated in the Exam ple 4 Com para tive Hexabromobenzene V-0 Yes Yes same manner as Sample No. 1, whereby 288 g of a bro 60 Exam minated cross-linked polymer was obtained. The bro ple 5 mine content of this polymer was 65.6%. Sample No. 4 Synthesis of a brominated linear poly styrene EXAMPLE 4 and COMPARATIVE EXAMPLE 6: 100 g of a polystyrene having a molecular weight of 65 Flame retardation of a polybutylene terephthalate 7,000 was dissolved in 2 liters of dichloroethane, and 5 A bromide (a bromine content of 63.5%) of a porous g of ferric chloride and 434 g of molecular bromine cross-linked polystyrene (a divinylbenzene content of were added. The mixture was reacted at room tempera 10% by weight) prepared in the same manner as in the 4,857,576 78 preparation of Sample No. 1, a polybutylene terephthal- TABLE 3________________ ate having an intrinsic viscosity of 0.85 (NOVADUR 5008 manufactured by Mitsubishi Chemical Industries, Flame retardation of a polyester Ltd.), antimny trioxide (manufactured by Mikuni Seiren Example 5 Comparative Example 6 K.K.), glass fiber (CS03 MA486A, manufactured by 5 Asahi Fiber Glass Co., Ltd.) and asbestos (R-244, manu Composition factured by Tomoe Kogyo K.K.) were mixed. By NOVADUR 5008 76.9% by weight (Br content: 4.6%) 76.9% by weight (Br content: 4.6%) means of an extruder equipped with a 40 mm <f> vent, the Flame retardant Brominated cross- Brominated poly* mixture was melt-kneaded and extruded at 250' C. to linked poly* styrene (Pyro- obtain pellets. The pellets were subjected to injection 10 molding by means of a 3.9 ounce injection molding machine (N-100B 25 Model, manufactured by The Sb203 GF styrene 2.9% (Br content: 1.9%) 5.2% 12.5% chek 68PB) 2.9% (Br content: 2.0%) 5.2% 12.5% Japan Steel Works, Ltd.), a test piece molding die pre Asbestos RG 244 2.5% 2.5% scribed in ASTM and a UL combustion test piece mold Flame retardancy ing die prescribed in UL-94, respectively, at a resin 15 UL 94 temperature of 260 C., At a die temperature of 80 C. UB test for an injection time of 10 seconds, a cooling time of 20 seconds (10 seconds in the case of the UL combustion i" 1/16" 1/32" V-0 V-0 V-0 V-2 V-2 HB test piece) and a retention time of 5 minutes, to obtain test pieces. The test pieces thus prepared, were sub 20 jected to flame retardancy tests in accordance with EXAMPLE 6 and COMPARATIVE EXAMPLES 8 UL-94 test method. The results thereby obtained are to 9: Flame retardation of Nylon 66 shown in Table 2. As Comparative Example 6, the test results of a case The bromide (a bromine content of 63.5%) of the wherein a non-cross-linked brominated polystyrene 25 porous cross-linked polystyrene employed in Example (Pyrochek 68 PB, manufactured by Nissan Ferro Or 4, Nylon 66 having an intrinsic viscosity of 302, NOVA- ganic Co., Ltd. and having a bromine content of from MID 3010J, manufactured by Mitsubishi Chemical In 65 to 67% by weight) was employed, are also shown in dustries, Ltd.) and antimony trioxide were mixed. By Table 2. means of a double-screw extruder, the mixture thereby 30 obtained was melt-keaded and extruded at 285 C., to TABLE 2 obtain pellets. Test pieces were prepared in the same Flame retardation of a polybutvlene terephthalate Example 4 Comparative Example 6 manner as in Example 4 except that the pellets were injection molded by means of a 3.9 ounce injection molding machine at a resin temperature of 280 C. (in Composition NOVADUR 5008 Flame retardant Sb203 GF Asbestos RG 244 Flame retardancy 69.8% by weight Brominated cross* linked poly* styrene 10.0% (Br content: 6.4%) 5.2% 12.5% 2.5% 69.8% by weight Brominated poly- styrene (Pyrochek 68PB) 10.0% (Br content: 6.7%) 5.2% 12.5% 2.5% 35 jection time: 10 seconds, cooling time: 20 seconds), and the test pieces were subjected to flame retardancy tests. Further, for the purpose of comparison, similar tests were conducted with respect to the cases wherein a noncross-linked brominated polystyrene (Pyrochek 68 40 PB) and decabromodiphenyl ether were employed. The results are shown in Table 4. TABLE 4 UL 94 UB test 1" 1/16" 1/32" Flame retardation of Nylon 66 Comparative V-0 V-0 45 Example 6 Example 8 V-0 V-l V-0 HB Composition NoVAMID 30I0J 72% 72% Flame retardant Brominated Brominated EXAMPLE 5 and COMPARATIVE EXAMPLE 7: 50 Flame retardation of a polyester cross*linked polystyrene 20.0% polystyrene 20.0% Pellets were prepared in the same manner as in Exam ple 4 except that a halogen-containing polyester resin Antimony tri- (Br content: 12.7%) 8.0% (Br content: 13.4%) 8.0% (NOVADUR 5208 manufactured by Mitsubishi Chemi oxide cal Industries, Ltd. and having a bromine content of 55 Flame retardancy 6%) prepared by the copolymerization of 1.0 mol of dimethyl terephthalate, 1.2 mol of 1,4-BG and 0.06 mol UL 94 Thickness 1" V-0 V-l of 2,2-bis(4-hydroxyethoxy-3,5-dibromophenyl)pro- pane and having an intrinsic viscosity of 0.85, was used Thickness 1/16" as the base resin. The blending ratios and the results of 60 Thickness 1/32" V-0 V-l V-2 HB Comparative Example 9 72% Decabromo* diphenyl ether 15.3% (Br content: 12.7%) 8.0% Defoaming and hardly molded " the flame retardancy tests conducted in the same man ner as in Example 4, are shown in Table 3. Further, a test was conducted in the same manner as in Example 5 except that a non-cross-linked brominated EXAMPLE 7 and COMPARATIVE EXAMPLES 10 to 11: Flame retardation of AAS polystyrene was used as the flame retardant instead of 65 A bromide (a bromine content of 65.3%) of a porous the brominated cross-linked polystyrene used in Exam cross-linked polystyrene used in Example 4, a polycar ple 5. The results are shown as Comparative Example 7 bonate (NOVALEX 7022A, manufactured by Mit in Table 3. subishi Chemical Industries, Ltd.) acrylonitrile-styrene- 4,857,576 9 10 acryl rubber (AAS, Vitax 6100A, manufactured by 5. The method according to claim 2, wherein said Hitachi Chemical Industries Co., Ltd.) and antimony monovinyl aromatic compound is styrene, and said trioxide, were mixed. Pellets were prepared in the same polyvinyl compound is divinylbenzene. manner as in Example 6 by melt-kneading the mixture at 6. The method according to claim 1, wherein said 270 C. The pellets were subjected to injection molding 5 brominated cross-linked vinyl aromatic polymer is pre under the same condition as in Example 6 to obtain test pared by brominating a cross-linked vinyl aromatic pieces. The test pieces were subjected to flame retard- polymer obtained by cross-linking a vinyl aromatic ancy tests. For the purpose of comparison, similar tests were conducted with respect to the cases wherein a non- 10 polymer. 7. The method according to claim 6, wherein the cross-linked vinyl aromatic polymer is obtained by cross-linking the vinyl aromatic polymer by a Friedel- crosslinked brominated polystyrene (Pyrochek 68PB) Crafts reaction. and decabromodiphenyl ether were employed, respec 8. The method according to claim 1, wherein said tively. The results are shown in Table 5. flammable polymer material is at least one resin selected Composition NOVALEX 7022A ASS Flame retardant TABLE 5 Flame retardation of ABS Example 7 Comparative Example 10 42.3% 42.3% Brominated cross-linked 42.5% 42.5% Brominated polystyrene Comparative Example 11 43.4% 43.4% Decabromodiphenyl ether 15 from the group consisting of a polyacetal, a polycarbon ate, a polyamide, a polyphenyleneoxide, a polysulfone, a polyarylate, a polyphenylene sulfide, a polyethyleneterephthalate, a polybutyleneterephthalate, a polymethacrylate, a polyethylene, a polypropylene, a 20 polystyrene, an acrylonitrile-styrene resin, an acrylonitrile-butadiene-styrene resin and a mixture thereof. 9. The method according to'claim 1, wherein said flame-resistant polymer material is prepared by incor porating from 0.1 to 40 parts by weight of said pow Antimony trioxide polystyrene 9.4% (Br content: 6.0%) 6.0% 9.0% (Br content: 6.0%) 6.0% 7.2% (Br content: 6.0%) 6.0% 25 dered, brominated, cross-linked vinyl aromatic polymer into 100 parts by weight of said flammable polymer material. 10. The method according to claim 9, wherein the quantity of said powdered, brominated, cross-linked Flame retardancv 30 vinyl aromatic polymer ranges from 3 to 30 parts by UL 9* Thickness i" Thickness 1/16" Thickness 1/32" V-0 V-0 V-2 V-l V-2 HB weight per 100 parts by weight of said flammable poly V-0 mer material. V-2 HB 11. The method according to claim 1, wherein said powdered, brominated, cross-linked vinyl aromatic 35 polymer is incorporated into said flammable polymer What is claimed is: material together with a flame retardant assistant which 1. A method for rendering a flammable polymer ma assists the flame retarding action of said brominated, terial flame-resistant, which comprises incorporating cross-linked vinyl aromatic polymer. into the flammable polymer material a powdered, cross- 12. A method for rendering a flammable polymer linked vinyl aromatic polymer brominated to contain 40 material flame-resistant, which comprises: from 30 to 70% by weight of bromine and optionally a incorporating into the flammable polymer material a flame retardant assistant, said brominated cross-linked powdered, brominated cross-linked styrene poly polymer being substantially non-meltable by heat, mer containing from 30 to 70% by weight bromine wherein said brominated cross-linked vinyl aromatic and optionally a flame retardant assistant, said bro polymer is prepared by (1) brominating a cross-linked 45 minated cross-linked polymer being substantially vinyl aromatic copolymer obtained by the copolymer non-meltable by heat, said brominated cross-linked ization of a monovinyl aromatic compound with a poly styrene polymer being prepared by brominating a vinyl compound, or (2) brominating a cross-linked vinyl cross-linked styrene polymer containing from 3 to aromatic polymer obtained by cross-linking a vinyl 50% by weight divinylbenzene monomer obtained aromatic polymer. 50 by copolymerizing styrene with divinylbenzene. 2. The method according to claim 1, wherein said 13. The method of claim 4, wherein said polyvinyl brominated cross-linked vinyl aromatic polymer is pre pared by brominating a cross-linked vinyl aromatic aromatic monomer is divinylbenzene, divinylxylene or trivinylbenzene, said polyvinyl heterocyclic compound copolymer obtained by the copolymerization of a monovinyl aromatic compound with a polyvinyl com pound. 55 is divinylpyridine or trivinylpyridine and said polyvinyl aliphatic monomer is ethylene glycol dimethacrylate or trimethylolpropane trimethacrylate. 14. A method for rendering a flammable polymer 3. The method according to claim 2, wherein the material flame-resistant, which comprises incorporating content of the polyvinyl compound in said cross-linked into the flammable polymer material a powdered, cross- vinyl aromatic copolymer is from 3 to 50% by weight. 60 linked vinyl aomatic polymer brominated to contain 4. The method according to claim 2, wherein said from 30 to 70% by weight of bromine and optionally a monovinyl aromatic compound is at least one member flame retardant assistant, said brominated cross-linked selected from the group consisting of styrene, vinyitolu- polymer being substantially non-meltable by heat, ene, vinylnaphthalene and a mixture thereof, and said wherein said brominated cross-linked vinyl aromatic polyvinyl compound is at least one member selected 65 polymer is prepared by (1) brominating a cross-linked from the group consisting of a polyvinyl aromatic mon vinyl aromatic copolymer obtained by the copolymer omer, a polyvinyl heterocyclic compound, a polyvinyl ization of a monovinyl aromatic compound with a poly aliphatic monomer and a mixture thereof. vinyl compound, or (2) brominating a cross-linked vinyl 11 aromatic polymer obtained by cross-linking a vinyl aromatic polymer, and the resulting flame-resistant ma terial has a flame retardancy of V-0 as measured by using a 1/16" test piece in accordance with UL-94 stan dards. 5 15. A method for rendering a flammable polymer material flame-resistant, which comprises: incorporating into the flammable polymer material a powdered, brominated cross-linked styrene poly mer containing from 30 to 70% by weight bromine 10 and optionally a flame retardant assistant, said bro- minated cross-linked polymer being substantially 12 non-meltable by heat, said brominated cross-linked styrene polymer being prepared by brominating a cross-linked styrene polymer containing from 3 to 50% by weight divinylbenzene monomer obtained by copolymerizing styrene with divinylbenzene, and the resulting flame-resistant material has a flame retardancy of V-0 as measured by using a 1/16" test piece in accordance with UL-94 stan dards. 16. The method according to claim 11, wherein the une retardant assistant is antimony trioxide. ***** 15 20 25 30 35 40 45 50 55 60 65