THERMOPLASTICS CONTAINING BROMINATED HOMOPOLYMER

Abstract: A flame retardant thermoplastic composition comprising a normally flammable thermoplastic base resin and a flame retarding additive comprising polymerized bromostyrene units, nominally characterized as a low molecular weight didromostyrene homopolymer.

Description: THERMOPLASTICS CONTAINING BROMINATED HOMOPOLYMER Background of the Invention This application is a continuation-in-part of copending application Serial No. 678,308, filed December 5, 1984, and hereby incorporated by reference. 1. Field of the Invention The present invention relates to flame retardant 10 compositions comprising a normally flammable thermoplastic base resin and a brominated alkenyl aromatic polymer additive containing polymerized dibro ostyrene. 2. Description of the Prior Art ] _5. There have been numerous attempts in the prior art to provide flame retardant thermoplastics. Typically, it has been necessary to heavily fill the thermoplastic base resin material with additives until the desired degree of flame retardancy has been 2o achieved. However, this offered several disadvantages in so far as a large proportion of additives could normally be expected to detract from the physical properties of the thermoplastic base resin. Furthermore, it was not unusual to require large 25 quantities of halogen-containing materials as well as metal compounds in some systems. It will be seen that the present invention provides improved flame retardant thermoplastic compounds which not only require a lower relative 30 proportion of halogen materials but also avoid the necessity of utilizing those organic halides and metal compounds which may be undesirable in certain applications. For example, where plate-out may be a problem in a molding process, compositions of the present invention offer sufficient flame retardance by providing an effective bromine content which is chemically bound within the polymer matrix. This typically allows a higher processing temperature for the flame retardant composition. The flam ability properties of most thermoplastics are very important physical properties which are evaluated in several ways and most typically in accordance with Underwriters Laboratory Bulletin Number 94. The UL-94 test protocol describes desirable V-0, 5-V, and HB ratings which are useful for many thermoplastics. Among the many attempts to develop flame retarding additives for thermoplastics there notably may be included organic phosphorus compounds, organic halides, and other halogen additives with or without metal synergists such as antimony oxide. It is noteworthy that polyvinyl chloride, for example, exhibits good flammability properties in certain applications because of its chlorine content. Each of the aforementioned flame retarding additives has been successfully utilized in certain applications but nonetheless exhibits disadvantagous properties to varying degrees. Brominated additives of various types also have been successfully used to flame retard thermoplastic materials. Included among these would be decabromodiphenyl ether, brominated polyphenylene ether, brominated polycarbonate oligomer, and brominated polystyrene. Silicones have also been utilized as flame retarding additives. See for example U.S. Patent 4,387,176 (Frye) . In a polyphenylene ether based system, Yonemitsu, et al. suggested the use of chlorinated styrene compounds to improve the flame retardancy of their compositions. In pending U.S. Patent Applications, S.N. 655,312 and 655,313 (Cooper et al ) bromostyrene copolymers were utilized to provide improved flame retardance in a polyphenylene ether system. And in U.S. Patent 4,279.808 (Hornbaker et al.) there is described a flame retardant thermoplastic composition formed by polymerization of nuclear brominated styrene in the presence of a rubbery polymer. All of the foregoing patents and applications are hereby incorporated by reference. Summary of the Invention The present invention provides flame retardant thermoplastic compositions. Such thermoplastic compositions embody a wide range of flammability properties, ranging from extremely flammable materials to those which are much less flammable even without a flame retarding additive. It is contemplated that the flame retarding additive described below can be utilized to some degree in all such thermoplastic resin systems. Each such system will require a relatively different effective amount of the flame retarding additive to achieve desired flammability properties. It is within the skill of the art to determine such effective amounts for the various thermoplastic resin systems described below. In general, however, it will be desirable for the flame retarding additive to provide approximately 0.5 to 30 weight percent bromine relative to the weight of thermoplastic base resin. Improved flame retardant properties will ordinarily be achieved within such a range. A smaller bromine content will not ordinarily show significant effect and a higher bromine content may exhibit other deleterious and undesired properties. The flame retarding additive utilized in the present invention is a brominated alkenyl aromatic polymer which contains units having the formula R wherein each R group represents, independently, hydrogen, a monovalent hydrocarbon radical, or halogen and said monomer units contain on the average, approximately, 1.5 to 2.5 bromine atoms per aromatic nucleus. A bromine content within this specified range has been found to be a particular useful means for delivering the required bromine content to the thermoplastic base resin to achieve desired flammability properties. Inasmuch as the bromine content per aromatic nucleus ranges from on the average 1.5 to 2.5 bromine atoms, applicants have chosen to characterize such materials as poly- dibromostyrene. A particularly preferred additive will be a homopolymer of dibromostyrene although in its broadest sense the present invention encompasses brominated alkenyl aromatic polymers which are polybromstyrene. A preferred additive will be comprised of monomer units having a general formula -C-C- wherein x represents, on the average, 1.5 to 2.5 bromine atoms per aromatic nucleus. It is noteworthy that at the present time it is not believed that aliphatic bromine plays any significant part in the additive for compositions of the present invention. Inparticular, a preferred flame retarding additive will be an alkenyl aromatic polymer having a general wherein n represents the average degree of polymerization and is an integer of, approximately, 5 to 350 and will typically range from, approximately, 5 to 70 monomeric units; x represents, on the average, 1.5 to 2.5 bromine atoms per aromatic nucleus. It can 5 be seen that the amount of bromine can be varied by several factors notably the amount of bromine substitution on the aromatic nucleus. Those skilled in the art will be o able to vary such factors to provide a variety of effective flame retarding additives which deliver the required amount.of bromine to the thermoplastic base resin system as noted above. In some applications it may be further desirable to combine the flame 5 retarding bromine additive with an effective amount of a synergistic metal compound such as an antimony oxide. Description of the Invention The flame retarding additive utilized in 0 compositions of the present invention can be nominally characterized as a "dibromostyrene homopolymer". The expression "dibromostyrene homopolymer" as used herein represents several aspects of the present invention. The additive is an alkenyl aromatic compound having bromine substituents preferably comprised of bromo-styrenic units. The compounds are labeled "dibro o" because a typical flame retarding additive of the present invention will have approximately but not necessarily, two bromine atoms per aromatic nucleus among the alkenyl aromatic units. That is to say a combination of mono, di, and tri brominated styrene onomeric units can yield a polymeric product having approxi atly dibromo substitution. Typically, the aliphatic bromine content, if any, will be minimal. The flame retarding properties of the additive will of course depend upon the ability of the additive to deliver an effective bromine content to the normally flammable thermoplastic base resin. It will now be possible to those skilled in the art to optimize the flame retardance of individual thermoplastic systems by manipulating the brominated alkenyl aromatic constituents and providing an effective flame retarding bromine content. As noted above, for many of these thermoplastics it is believed that an approximately dibro osubstituted homopolymer will perform adequately and in many cases deliver excellent results. Futher optimization may be possible in designing dibromostyrene homopolymer systems where not only does the degree of bromine subsitution vary but the position of the bromine atoms on the aromatic nucleus may be varied also. It is contemplated that all such variations which deliver effective, approximately dibromoho opolymer are all average approximately 2 bromine substitutents per monomer unit) . It is well known that alkenyl aromatic compounds readily polymerize with other polymerizable materials, to produce dibromostyrene copolymers. It is also contemplated that effective flame retarding agents of the present invention can be provided even if a number of other monomeric units (such as styrene monomer, 4-methylstyrene or acrylonitrile) are also included. Such products would technically be considered copolymers but for purposes of the present invention are included within the scope of the essentially dibromohomopolymer flame retarding additives. Inclusion of other polymerizable species to provide copolymers would not detract from the scope of the present invention. These additives will find greatest utility in delivering effective bromine flame retardants by virtue of the typical "dibromohomopolymer" monomeric units. The degree of polymerization of the additive polymer can be adjusted to provide flame retarding additives having varying molecular weights.This will further assist those skilled in the art in designing thermoplastic compositions having the required amount of brominated flame retarding additive for useful compositions. It is expected that polymers of different molecular weights will find utility in the various intended thermoplastic base resins. As noted above, the degree of polymerization could vary within a wide range, typically from about 5 to 350 units on the average. Such flexibility in developing the flame retarding additive will be especially useful in designing a product which has the desirable bromine content for effective flame retardance and shows sufficient compatibility with the thermoplastic base resin while at the same time does not unduly detract from other physical properties of the composition. It is contemplated that the brominated flame retarding additive described above will find great utility in a variety of thermoplastic base resins which may include but are not limited to the following: Styrenics including polystyrene and rubber-modified polystyrene, acrylonitrile-butadiene-styrene terpoly er, styrene-acrylonitrile copolymer,and styrene-maleic anhydride copolymer. Polyphenylene ether resins and copolymers including polyphenylene ether resins modified with styrenic resins such as high impact polystyrene; including NORYL resins manufactured by General Electric Company. Polyarylates including polycarbonates such as LEXAN resins manufactured by General Electric Company, as well as blends of polycarbonate and ■styrene-maleic anhydride copolymer. Polyesters such as polybutylene terephthalate and polyethylene terephthalate including VALOX resins manufactured by General Electric Company and including blends of polycarbonate and polybutylene terephthalate. Terpoly ers of acrylonitrile-styrene-acrylate such as the GELOY resins manufactured by General Electric Company and in particular combinations of a crosslinked aerylate, a crosslinked styrene-acrylonitrile and an uncrosslinked styrene-acrylonitrile. Polyolefins such as polyethylene including high, low, and linear low density polyethylene; and polypropylene, etc. Polyacrylates and polyurethanes which can be flame retarded with the dibromohomopolymer of the present invention. Polyetherimides such as ULTEM resins manufactured by General Electric Company. Polysulfone resins such as those manufactured by Union Carbide Company. Polya ides as a class including Nylons and polycaprolactams, such as Nylon 6, Nylon 6,6 and Nylon 12 etc. It is also contemplated that the flame retarding additive of the present invention may find utility in such other polymeric systems such as polyorganosiloxanes, iono ers, acetal resins, ethylene vinyl acetate, polymethylpentene, flexible PVC, as well as, natural and synthetic rubber systems such as Monsanto SANTOPRENE. A flame retarding additive of the present invention can be conventionally added to the thermoplastic base resin by any suitable means such as a Banbury mixer, twin roll mixer, or extruder. Typically the components will be mixed together in a dried form at room temperature and extruded at elevated temperature to provide a uniform product. Flame-retardant thermoplastics of the present invention can be molded, such as by injection, foam or blow molding, or extruded into final products. Those skilled in the art will be able to optimize such thermoplastic compositions with conventional filler and reinforcing filler materials as well as pigments, processing aids, plasticizing agents and flow promoters, antioxidants and other conventional additives. Metal synergists can be utilized for certain compositions. These include antimony, lead, zinc and molybdenum compounds such as oxides, phthalates, borates etc. In the following examples all parts are by weight unless otherwise indicated. Example 1 Preparation of Polydibro ostyrene A bromostyrene polymer was produced by thermally polymerizing a mixture of 50% toluene, 3.85% monobromostyrene, 42.5% dibromostyrene, and 3.65% tribromostyrene in a reactor train. The reactor train consisted of nine heated, agitated zones. The temperature of the reactor zones were in order (degrees centigrade): 67, 74, 75, 82, 84, 85, 98, 112, 129. The reactor feed was continuously pumped through the reactor train with an average residence time of 10.2 hours. The product from the reactor train was pumped to a devolatilizing extruder to remove toluene and unreacted monomer. The recovered polymer had 105,000 Mw (weight average molecular weight) and 47,700 Mn (number average molecular weight) as measured by GPC based on monodisperse polystyrene standards. EXAMPLE IB Preparation of Polydibromostyrene A bromostyrene polymer was prepared by passing a mixture consisting of 6.93% monobromostyrene, 76.5% dibromostyrene, 6.56% tribromostyrene, and 10% toluene through a heat exchanger operated at 190°C and 50 psi. The resulting polymer was devolatilized in an extruder. The polymer had 20,000 Mw and 7,700 Mn as measured by GPC based on monodisperse polystyrene standards. Example 2 Flame Retardant Polyphenylene Ether Resin Compositions A Mixture of 35 parts poly (2,6-dimethyl 1,4-phenylene) ether 65 parts rubber modified polystyrene 15 parts dibromostyrene homopolymer (additive 1A above) 4.5 parts antimony oxide 5 parts Kraton 1101 styrene-butadiene copolymer 1.5 parts polyethylene 0.15 parts zinc sulfide 0.15 parts zinc oxide were extruded in a 28 mm twin screw extruder and injection molded into standard test pieces. The test results below show that this blend has a good combination of mechanical properties and flame resistance. Flow channel 13.0 Tensile yield 6.7 Izod 4.4 Gardner 19 Heat Distortion Temperature 229 UL-94 V-0 Tensile elongation 62 Description of Tests: HDT: Heat-deflection temperature (°F) under 264 psi; 1/4" x 1/2" x 5" specimen FC: Flow channel (in.) _ ca. 570°F melt, 150°F mold, 10,000 psi injection pressure IZOD: Notched Izod impact (ft.-lbs/in.-n. ) ; 1/8" x 1/2" x 2 1/2" GARD: Gardner (falling dart) impact (in.-lbs) 1/8" x 4" disc TYS,TUS,TE: Tensile yield strength kpsi) , tensile ultimate strength kpsi) , tensile elongation; 1/8" x 8 1/2" (1/2" wide gauge length)% 1/8" UL94: Average self-extinguishing time (sec.) for five 1/8" x 1/2" x 2 1/2" specimens. (1/16" UL94 employs a 1/16" x 1/2" x 5" bar) when tested in accordance with Underwriters Laboratories Bulletin (4 procedures. Suffixes are UL94 V-ratings which the sample test results satisfy. Example 3 PPE/HIPS /Homopolymer Blends Composition (pbw) PPE HIPS ME112 KRAO A433B K1101 KG1652 1 35 65 11.7 3.5 7.5 2.5 2.5 2 40 60 11. 7 3.5 7.5 2.5 2.5 3 40 60 15.4 4.5 7.5 5.0 2.5 Note : Each sample also contains 0.15 ZnS , 0.15 ZnO Measured Properties ' -' HDI ___ IZOD GARD IYS IE 1/16"UL94 1 190 21.3 4.7 18 5.9 65 4.9.V-0 2 199 19.0 5.1 24 6.2 65 4.0, V-0 3 199 19. 3 4.8 15 6.3 67 2.3.V-0 Descript: ion I of the Mater ials : KRAO is antimony oxide MB112 is a homopolymer of dibromostyrene having Mn=7,700; Mw = 20,000; % Br=58.4 (See Example IB above) A433B is an oligomeric polyester based upon aromatic dibasic acid and aliphatic glycol, sold as Admex KG1652 is Shell's triblock copolymer of styrene and post-hydrogenated butadiene (SEBS) , sold as Kraton G Example 4 100 parts crystal polystyrene (available commercially as DYLENE 8G) was combined with 20 parts dibromostyrene homopolymer (prepared in Example 1A) and six parts S 2 0, to provide a flame retarded composition. Test specimans 1/8" thick were molded along with a crystal polystyrene control. After a 10 second ignition, the flame retarded composition self-extinguished in one second. The control dripped after 25 seconds, following a 10 second ignition period. Total burn time for the control exceeded 100 seconds. Example 5 100 parts high impact polystyrene (available commercially as AH1897 from American Hoeschst) was combined with 20 parts of the dibromostyrene homopolymer prepared in Example 1A above and 6 parts Sb_0, to provide a flame retarded composition. Test specimans 1/8" thick were molded along with a high impact polystyrene control. After a 10 second ignition the flame retarded high impact polystyrene composition self-extinguished in one second. The control dripped after 5 to 38 seconds, following a ten second ignition, and had a total burn time exceeding 100 seconds in each case. Example 6 100 parts polycarbonate resin (available commercially as LEXAN 141) was combined with 10 parts of the dibromostyrene homopolymer (prepared in Example 1A above) to provide a flame retarded polycarbonate composition. Test specimans 1/8" thick were molded along with a polycarbonate control. The flame retarded polycarbonate composition met the requirements for a UL-94 V-0 rating. Control samples dripped after 13 to 20 seconds, respectively, and had total burn times of 14 to 20 seconds. Example 8 100 parts of an acylonitrile-butadiene-styrene terpolymer (available commercially as CYCOLAC T) was combined with 40 parts dibromostyrene homopolymer (prepared in example 1A above) and 6 parts Sb-,0-. to provide a flame retarded ABS composition. Test specimans 1/8" thick were molded along with an ABS control. The flame retarded ABS compositions met the requirements of UL Bulletin 94 for a V-0 rating. The controls specimans failed the test with flaming drips. Example 9 100 parts of an aerylonitrile-styrene-acrylate interpolymer composition was flame retarded with 40 parts of the dibromostyrene homopolymer (prepared in Example 1A above) and 6 parts Sb-0-. This flame retarded ASA was compared with a control available commercially as GELOY 1120. After a ten second ignition the flame retarded compositions self-extinguished in 0 to 1 seconds and met the requirements for a UL-94 rating of V-0. Control samples exhibited drips and had total burn times in excess of 200 seconds. Example 10 100 parts of a polystyrene-maleic anhydride resin (available commercially as DYLARK 350) was combined with 30 parts of the dibromostyrene homopolymer (prepared in Example 1A above) and 6 parts Sb 2 0 3 to provide a flame retarded composition. Test specimans 1/8" thick were molded along with a control sample. The flame retarded polystyrene-maleic anhydride copolymer met the requirements of UL-94 for a V-0 rating. The control samples experienced drips and had total burn times of from 290 to 310 seconds. Example 11 100 parts polyamide resin (available commercially as ZYTEL 101 resin, a NYLON 6,6) was combined with 25 parts of the dibromostyrene homopolymer (prepared in Example 1A above) and 6 parts Sb-0, to provide a flame retarded composition. Test specimans 1/8" thick were molded along with a polyamide control. The flame retarded polyamide compositions exhibited some flaming drips and total burn times of approxmately 20 seconds, however, the polyamide control samples exhibited flaming drips and total burn times ranging from 170 to 200 seconds. It is apparent that the dibromostyrene homopolymer shows an effect in a polyamide system but further optimization is required.

Claims: Claims 1. A flame retardant thermoplastic composition comprising: (a) a normally flammable thermoplastic base resin; and (b) a flame retarding amount of an additive wherein said additive is a brominated alkenyl aromatic polymer containing monomer units of the formula R wherein each R group represents, independently, hydrogen, a monovalent hydrocarbon radical, or halogen and said monomer units contain on the average, approximately, 1.5 to 2.5 bromine atoms per aromatic nucleus. 2. A composition as in Claim 1 wherein said brominated alkenyl aromatic polymer is polybromostyrene homopolymer. 3. A composition as in Claim 2 wherein said flame retarding additive is a homopolymer of dibromostyrene. 4. A composition as in Claim 1 wherein said additive is comprised of monomer units consisting essentially of monomer units having a general formula x represents, on the average, 1.5 to 2.5 bromine atoms per aromatic nucleus. A composition as in Claim 1 wherein said flame retarding additive is an alkenyl aromatic polymer having a wherein age degree of polymerization and is an integer of, approximately,5 to 350 and X represents on the average 1.5 to 2.5 bromine atoms per aromatic nucleus. A composition as in Claim 5 wherein said brominated flame retarding additive has a degree of polymerization of approximately 5 to 70 units. A composition as in Claim 1 wherein said brominated flame retarding additive provides, approximately, 0.5 to 30 weight percent bromine based upon the weight of said thermoplastic base resin. A composition as in Claim 1 wherein said composition further comprises an effective amount of synergistic metal compound.

Inventors: AYCOCK DAVID FREDERICK, HAAF WILLIAM ROBERT, LEE GIM FUN JR, AYCOCK, DAVID, FREDERICK, HAAF, WILLIAM, ROBERT, LEE, GIM, FUN, JR.
Applicants: GEN ELECTRIC, GENERAL ELECTRIC COMPANY
Application year: 1985
Main classification: C08L101
IPC codes: C08L101