United States Patent (19) 11 Patent Number: 4,510,280 Jones et al. 45) Date of Patent: Apr. 9, 1985

54 THERMOPLASTIC PVC MOLDING COMPOSITIONS OTHER PUBLICATIONS Journal of Polymer Science-vol. 21, pp. 791-796, (75) Inventors: Jesse D. Jones; Edwin D. Hornbaker, (1977)-Fava et al. both of Baton Rouge, La. Primary Examiner-Carman J. Seccuro Attorney, Agent, or Firm-Donald L. Johnson; John F. Assignee: Ethyl Corporation, Richmond, Va. Sieberth Appl. No.: 209,843 57 ABSTRACT Blends of (a) a vinyl chloride polymer having a relative Filed: Nov. 24, 1980 viscosity as measured at a concentration of 1 gram per 100 grams of cyclohexanone at 25 C. falling within the Int. Cl...... C08L 27/06; C08L 25/08; range of about 1.50 to about 1.85; (b) a copolymer of a C08L 51/04; C08L 55/02 vinyl aromatic compound and an ol,£3-unsaturated cyc U.S. Cl...... 524/178; 524/179; lic anhydride in which the relative proportions of said 524/180,524/504; 525/71; 525/74; 525/207; compound and said anhydride fall within the range of 525/192 about 91 to about 70 weight percent of said compound Field of Search ...... 525/207, 74, 71; and about 9 to about 30 weight percent of said anhy 260/45, 75 K. 524/180, 178, 179 dride; and (c) a tin-containing stabilizer and an impact modifier for vinyl chloride polymers. These blends References Cited contain 60 to 40 weight percent of (a) and 40 to 60 U.S. PATENT DOCUMENTS weight percent of (b) and have an Izod impact strength

3,626,033 2/1971 Keskkula et al...... 260/876 R (ASTM D256, Method A) of at least 0.5 foot pound per 3.632,839 1/1972 Young et al...... 52.5/207 inch; a heat deflection temperature (ASTM D 648) at 66 3,919,354 A1975 Moore et al...... 524/244 psi of at least 75° C.; and a dynamic thermal stability of at least 10 minutes. FOREIGN PATENT DOCUMENTS 1297505 11/1972 United Kingdom. 16 Claims, No Drawings 4,510,280 1. 2 91 to about 70 weight percent of said compound and THERMOPLASTC PVC MOLDING about 9 to about 30 weight percent of said anhydride; COMPOSITIONS and (c) a tin-containing stabilizer and an impact modi fier for vinyl chloride polymers; with the proviso that This invention relates to vinyl chloride polymer com 5 the blend contains 60 to 40 (preferably 55 to 45) weight positions of enhanced performance characteristics. percent of (a) and 40 to 60 (preferably 45 to 55) weight percent of (b) and the further proviso that the blend has BACKGROUND the following properties; (d)an Izod impact strength Vinyl chloride resins are widely used in the manufac (ASTM D256, Method A) of at least 0.5 foot pound per ture of various useful end products, including moldings, O inch; (e) a heat deflection temperature (ASTM D 648) tile, pipe, sheets, film, bottles, and the like. Unfortu at 66 psi of at least 75 C.; and (f) a dynamic thermal nately, unplasticized vinyl chloride resins used in the stability of at least 10 minutes. manufacture of rigid end products tend to have poor The procedure used to measure dynamic thermal heat deformation characteristics. Consequently, they stability is as follows: A Brabender Plasticorder fitted are unsuitable for use in certain areas of application 15 with a No. 6 mixing head heated to 190° C. is charged where structural integrity under heat and load is of with 60 grams of the formulation to be tested, with the prime importance. rotor speed being held constant at 150 rpm after charg Heretofore, attempts have been made to improve ing. The test is continued at 190° C., with 150 rpm rotor upon the relatively poor heat deformation characteris speed, until the torque increases by 200 meter-grams tics of polyvinyl chloride resins. For example, in U.S. 20 above the equilibrium torque (which is the constant Pat. No. 3,626,033 ternary compositions are described torque value attained following the initial substantial in which comprise 50 to 75 weight percent of a vinyl torque increase observed during fusion of the formula chloride resin, 10 to 35 weight percent of a polydiene tion). The dynamic thermal stability is expressed as the rubber nitrile graft copolymer and 15 to 35 weight per time from charging of the sample until this 200 meter cent of an anhydride-containing copolymer, such as 25 grams torque increase has occurred. Thus the longer styrene-maleic anhydride. the time, the higher the dynamic thermal stability. British Pat. No. 1,297,505 discloses that small In a preferred embodiment of this invention, the amounts of certain copolymers such as styrene-maleic blend is made from a rubber-modified thermoplastic anhydride can be admixed with polyvinyl chloride ho copolymer of a vinyl aromatic compound and an af3 mopolymer to improve impact strength of the end prod 30 unsaturated cyclic anhydride. Here again the relative uct. The amount of such anhydride copolymer used proportions of the vinyl aromatic compound and the ranges from 0.1 up to 5 parts by weight per 100 parts by af3-unsaturated cyclic anhydride in the resin phase of weight of the PVC homopolymer. Although tensile the copolymer fall within the range of about 91 to about impact strength of the PVC is shown to be improved by 70 weight percent of the vinyl aromatic compound and this means, nothing is said about the heat deformation 35 about 9 to about 30 weight percent of the cyclic anhy characteristics of the resultant binary blends. dride, but in this case the graft copolymer contains up to In Journal of Applied Polymer Science, Vol. 21, pages about 33 parts (preferably 25 parts or less) by weight of 791-796 (1977), the results of torsional pendulum analy the rubber per 100 parts by weight of the copolymer ses are set forth for a 50:50 blend of polyvinyl chloride itself, and styrene-maleic anhydride copolymer. At page 795 Hence this invention also provides thermoplastic the authors point out that this blend is opaque and brit molding compositions which comprise in intimate ad tle, bearing all the marks of incompatability. The sty mixture: (a) a vinyl chloride polymer having a relative rene-maleic anhydride copolymer used in this experi viscosity as measured at a concentration of 1 gram per mental work was Dylark 232 from ARCO/Polymers, 100 grams of cyclohexanone at 25 C. falling within the Inc. which is understood to contain 92 percent by 45 range of about 1.50 to about 1.85; (b) a thermoplastic weight of styrene and 8 percent by weight of maleic rubber-modified graft copolymer of a vinyl aromatic anhydride. It is rubber free. compound and an ag-unsaturated cyclic anhydride in which the relative proportions of said compound and THE INVENTION said anhydride fall within the range of about 91 to about It has now been discovered that blends of vinyl chlo 50 70 weight percent of said compound and about 9 to ride polymers and copolymers of the styrene-maleic about 30 weight percent of said anhydride, and in which anhydride type can be produced having a number of the graft copolymer contains up to 33 (preferably up to superior performance characteristics, including in about 25) parts by weight of the rubber per 100 parts by creased resistance to heat deformation under load, and weight of the copolymer; and (c) a tin-containing stabi flame resistancy, as well as other properties desired in 55 lizer and an impact modifier for vinyl chloride poly thermoplastic molding compositions. These new com mers; with the proviso that the blend contains 60 to 35 positions are readily produced by known blending pro (preferably 55 to 40) weight percent of (a) and 40 to 65 cedures and require no special preparatory techniques (preferably 45 to 60) weight percent of (b); and with the or precautions. further proviso that the blend has the properties in ac The thermoplastic molding compositions of this in 60 cordance with (d), (e), and (f) presented hereinbefore. vention comprise in intimate admixture (a) a vinyl chlo Component (a), the vinyl chloride resin, may be a ride polymer having a relative viscosity as measured at homopolymer of vinyl chloride or a copolymer of vinyl a concentration of 1 gram per 100 grams of cyclohexa chloride with a minor portion of one or more monomers none at 25 C. falling within the range of about 1.50 to copolymerizable with vinyl chloride. In such copoly about 1.85; (b) a thermoplastic copolymer of a vinyl 65 mers vinyl chloride comprises on a weight basis at least aromatic compound and an ol,6-unsaturated cyclican about 90 percent of the copolymer and the copolymer hydride in which the relative proportions of said com izable monomer comprises up to about 10 percent. A pound and said anhydride fall within the range of about wide variety of copolymerizable monomers may be 4,510,280 3 4. used to prepare such vinyl chloride copolymers. These preferred. Styrene itself is the most preferred vinyl include vinylidene chloride; vinyl acetate and vinyl aromatic compound. stearate; acrylic and methacrylic acid esters; olefins The cyclic anhydride compounds of component (b) such as ethylene, propylene, isobutylene and the like; are preferably ag-unsaturated dicarboxylic anhy vinyl alkyl ethers such as vinyl isobutyl ether, vinyl drides. For example, the term cyclic anhydride identi lauryl ether and vinyl cetyl ether; acrylic acid and fies anhydrides having the formula: methacrylic acid; acrylonitrile and methacrylonitrile; diethyl fumarate; maleic anhydride; dimethyl itaconate; O O O styrene; N-vinyl carbazole; N-vinyl pyrrollidone; allyl s1S. Naa compounds such as allyl chloride; diolefins such as O butadiene, isoprene, chloroprene and the like; or mix R7-CH - eac--(CH2)-R8 tures thereof. Further, the vinyl chloride resins include halogenated polyvinyl chloride and the like. wherein the dash lines represent a single or a double Methods for the preparation of vinyl chloride poly carbon-to-carbon bond, R7 is selected from the group mers are well known in the art and reported in the 15 consisting of hydrogen, alkyl or aryl radicals containing literature. See for example Kirk-Othmer, Encyclopedia up to 8 carbon atoms, R8 is selected from the group of Chemical Technology, Second Edition, Interscience consisting of hydrogen, vinyl, alkyl, alkenyl, alkylcar Publishers, Volume 21, pages 369-412 (Copyright boxylic or alkenylcarboxylic of from 1 to 12 carbon 1970), the disclosure of which is incorporated herein. atoms and n is an integer of from 0 to about 10. Exam Vinyl chloride polymers having suitable relative viscos 20 ples include maleic anhydride, methyl maleic anhy ities for use in the practice of this invention are available dride, dimethyl maleic anhydride, citraconic anhydride, from a number of commercial suppliers. For best results itaconic anhydride, phenylmaleic anhydride, aconitic the relative viscosity (as measured at a concentration of anhydride, and mixtures thereof. Maleic anhydride is 1 gram per 100 grams of cyclohexanone at 25 C.) of the the preferred anhydride of component (b). vinyl chloride resin should fall within the range of Copolymers of vinyl aromatic compounds and d.f3 about 1.50 to about 1.65 and accordingly the use of such unsaturated cyclic anhydrides which can be used in the vinyl chloride resins is preferred. Polyvinyl chloride practice of this invention are described in U.S. Pat. Nos. homopolymer resins falling within this relative viscos 2,769,804; 2,971,939 and 3,336,267, the disclosures of ity range are particularly preferred. which are incorporated herein by reference. Component (b), copolymers of a vinyl aromatic com 30 As noted above, these copolymers can be and prefer pound and an ag-unsaturated cyclic anhydride, are ably are rubber-modified copolymers. In preparing also well known in the art and are described in the these rubber-modified copolymers use of such rubbers literature. In general, they may be prepared by conven as polybutadiene, isobutylene-isoprene copolymers, tional bulk or solution techniques using free-radical styrene-butadiene copolymers, butadiene-acrylonitrile initiation. For example, styrene-maleic anhydride co 35 copolymers, ethylene-propylene copolymers, polyiso polymers can be obtained by simply reacting the two prene, ethylene-propylene-diene monomer terpolymers monomers, i.e., styrene and maleic anhydride, at 50 C. (EPDM) and the like can be employed. In this connec in the presence of benzoyl peroxide. The rate of poly tion see U.S. Pat. No. 3,919,354, the disclosure of which merization may be better controlled if a solvent such as is incorporated herein by reference. acetone, benzene, toluene or xylene is used. Component (b) copolymers whether rubber-modified Vinyl aromatic compounds of component (b) can be or not comprise from about 91 to about 70 parts by compounds of the formula: weight of vinyl aromatic monomer and from about 9 to about 30 parts by weight of the ol,6-unsaturated cyclic anhydride copolymerized therewith. Preferred poly CRECHR2 45 mers include those wherein the relative proportions of the styrene and the anhydride fall within the range of from about 86 to about 80 weight percent of the styrene R3 monomer and from about 14 to about 20 weight percent 50 of the anhydride monomer. Preferred rubber-modified R5 R4 copolymers used herein contain about 5 to 25 (most preferably 10 to 22) parts by weight of the rubber per where R and R2 are independently selected from the 100 parts by weight of the styrene/anhydride copoly group consisting of alkyl groups of from 1 to 6 carbon mer, although lesser amounts, even down to trace atoms and hydrogen; R3, R', R5 and R6 are indepen 55 amounts of rubber, are feasible. dently selected from the group consisting of chloro, The tin containing stabilizer utilized in the blends of bromo, hydrogen and alkyl of from 1 to 6 carbon atoms; this invention is susceptible to considerable variation and two of R, R', R5 and R6 may be concatenated and involves use of materials well known and readily together with hydrocarbyl groups to form a naphthyl available in the art. Examples of suitable tin stabilizers group in which the vinylic substituent is preferably in 60 include di-n-alkyl tin mercaptides, di-n-alkyl tin dilau the 1-position. All such compounds are free of any rates, dibutyl tin dimaleate, dibutyl tin lauryl mercap substituent that has a tertiary carbon atom. Preferred tide, di-octyl tin-S,S'-bis-(isooctylmercaptoacetate), vinyl aromatics are the styrenes, i.e., compounds in dibutyl tin bis-isooctylthioglycolate, di-(n-octyl) tin which R2 is hydrogen and R3, R“, R5 and R6 are inde maleate polymer, dibutyl tin mercaptopropionate, and pendently hydrogen, alkyl of 1 to 6 carbon atoms, 65 the like. These and other such tin stabilizers are known chloro or bromo. Of these compounds, styrenes in thermal stabilizers for polyvinyl chloride. The amount which R1 is hydrogen or methyl and R3, R4, R5 and R6 of the tin stabilizer used can be varied. Normally the are independently hydrogen, methyl or ethyl are most amount will range from about 1 to about 4 phr-i.e., 4,510,280 5 6 about 1 to about 4 parts by weight per 100 parts by small proportions of both materials may prove satisfac weight of (a) and (b). tory. Among the suitable materials for use as impact modi Flame retarding additives which may be used in the fiers, the other essential ingredient of the blends of this compositions of the invention comprise a large number invention, are styrene-methyl methacrylate grafted on of chemical compounds which are well known to those butadiene (MBS), acrylonitrile-styrene grafted on buta skilled in the art. In general, they contain chemical diene (ABS), styrene-acrylonitrile grafted on EPDM, elements which are used because of their flame-retard styrene-methyl methacrylate-acrylonitrile grafted on ing capacity, for example bromine, chlorine, antimony, butadiene (MABS), chlorinated polyethylene, methyl phosphorus and nitrogen. Preferably, the flame-retard methacrylate or methyl methacrylate-styrene grafted 10 ing additives are inorganic compounds which are nor on a polyacrylate such as polybutylacrylate, vinyl chlo mally effective in combination with halogenated or ride grafted on ethylene-ethyl acrylate copolymer, ganic compounds. These are materials such as antimony vinyl chloride grafted on butyl rubber, vinyl chloride compounds (e.g., antimony trioxide), zinc compounds grafted on EPDM, ethylene/vinyl acetate copolymers, (e.g., zinc borate), antimony-zinc complex compounds ethylene/acrylic acid copolymers (having some of the 15 (e.g., Oncor 75RA, a product of NL Industries, Inc.), acid functions neutralized), ethylene/methacrylic acid iron compounds (e.g., ferric oxide), and other metal copolymers (having some of the methacrylic acid func based inorganic compounds which perform well with tions neutralized), ethylene/alkyl acrylate/methacrylic antimony oxide (e.g., Ongard 2, a product of NL Indus acid terpolymer (also having some of the methacrylic tries, Inc.). When using a flame retardant, the amount acid functions neutralized), oxidized polyethylene, sty should be sufficient to yield a blend having a UL 94 rene-butadiene-styrene (S-B-S) block copolymers, rating of V-1 or better using test bars 0.060 inch thick. styrene/butadiene multiblock copolymers, styrene/- Smoke suppressing additives may also be used. Exam butadiene radial block copolymers, hydrogenated S-B-S ples include alumina trihydrate, cuprous cyanide, and block copolymers, styrene/butadiene rubber, acrylic combinations of nickel carbonate and zinc oxide. Or rubbers, EPDM, ethylene/methyl acrylate copolymers, 25 ganic phosphites and phenolic compounds exemplify ethylene/ethyl acrylate copolymers, and the like. These suitable antioxidants. materials are available in a wide range of molecular The compositions of the invention may be prepared weights and it is generally desirable that the impact by blending the components in a mixer (e.g., a Henschel modifier have a melt viscosity close to that of the sub mixer) and compounding the mixture on an extruder strate. Amounts of impact modifiers generally fall 30 (e.g. a Buss Ko-Kneader, a Farrel Continuous Mixer or within the range of from about 5 to about 20 phr. a Werner-Pfleiderer compounding extruder). Thereaf The blends of this invention can also include other ter, the extrudate is chopped into pellets and molded on ingredients, such as processing aids, lubricants, pig an injection molding machine. ments, flame retardants, smoke retardants, antioxidants, The present invention is further illustrated in the and the like, for their conventionally employed pur 35 following examples, which are not to be construed as poses. limiting. Processing aids of various types are entirely suitable EXAMPLE I for use in the blends of this invention. For example, use may be made of such polyvinyl chloride processing aids 40 Five different blends of this invention were prepared as those made from copolymers of methyl methacrylate using a commercial grade of PVC and five different and styrene, terpolymers of methyl methacrylate, lower styrene-maleic anhydride copolymers obtained from alkyl acrylate and acrylonitrile, or terpolymers of ARCO/Polymers, Inc. The copolymers were as fol methyl methacrylate, lower alkyl acrylate and dialky lows: itaconate, and the like. The preferred processing aids 45 are methyl methacrylate-lower alkyl acrylate copoly OKB-134 Unmodified; 17% maleic anhydride ners having a small portion (e.g., 3 to 15 percent) of the OKB-290 Unmodified; 25% maleic anhydride lower alkyl acrylate comonomer and having an inher OKB-332 Unmodified; 14% maleic anhydride OKB-350 Rubber-modified; 75.7% styrene, ent viscosity as measured at a concentration of 0.25 12.3% maleic anhydride, 12% rubber grams per 100 milliliters of chloroform at 25 C. of at 50 (i.e., 86% styrene-14% maleic least 0.1 and preferably 0.5 or higher. A variety of such anhydride copolymer containing 13.6 processing aids, including the preferred types, are avail phr rubber) able from various commercial sources. The amount of OKB-218 Rubber-modified; 74.7% styrene, 15.3% maleic anhydride, 10% rubber processing aid will generally range from about 0.5 to (i.e., 83% styrene-17% maleic about 10 phr. 55 anhydride copolymer containing 11.1 Typical lubricants which may be used in the blends of phr rubber) this invention include metal soaps, stearic acid, glyceryl monostearate, ethyl diaminostearate, paraffin and low The PVC and the respective copolymers were mechan molecular weight waxes, and the like. Conventional ically blended in equal proportions by weight employ pigments used in polyvinyl chloride may likewise be 60 ing a formulation used in making proprietary tin-stabil used in the blends of this invention in conventional ized PVC compositions. The proportions of the materi amounts. Ordinarily the concentration of lubricant and pigment will not exceed about 10 phr. als used in these five respective blends were as follows: If desired, small amounts of reinforcing fibers such as carbon filaments, asbestos, titanate whiskers, and glass 65 fiber may be employed. The amount of such materials Parts by Weight Components should not exceed about 10 phr. Ordinarily such rein SO Polyvinyl Chloride forcing fiber would be used in lieu of a filler although 50 Styrene-Maleic Anhydride Copolymer 4,510,280

-continued -continued Parts by Weight Components Injection Pressure Maximum Hold Pressure 1300 psi 2 T Stabilizer - Back Pressure 400 psi 4.5 Lubricants 5 12 Impact Modifier (MBS-type)

Styrene-Maleic Anhydride Copolymer Used None (Control) DKB-134 DKB-134 DKB-290 DKB-332 DKB-350 DKB-218 Amps 6.6 6.8 7.2 7.2 7.O 7. 7.2 Screw Recovery 14 10 O 10 O 9 9 Time Spiral Flow, 7.75 18.25 19 18.25 16.75 3.5 13.5 inches

32 CaCO3Processing Reinforcing Aid Filler The physical properties of these blends are shown in Table I. TABLE I Physical Properties of Blends None (Controi) DKB-134 DKB-134 DKB-290 DKB-332 DKB-350 DKB-218 Specific Gravity 1.3S 1,198 1205 1.223 1.260 1.186 20 Tensile-Yield, psi 5720 6750 6820 6440 6360 4650 5200 Tensile East. Mod, 353 419 399 400 421 295 331 10 psi Elongation, % O 10 7.5 8.7 6.7 6.9 8.8 Flexural Strength, psi 0,300 11,400 12,000 10,600 1,400 8,300 9,50 Flex. East. Mod. 337 381 384 384 380 299 277 10 psi Izod Impact, ft-lbs/in. inch bar 7.70 0.60 0.60 0.50 0.60 1.00 0.80 inch bar 5.80 0.70 0.60 0.50 0.50 1.20 1O Heat Deflection Temperature. C. at 264 psi 65 74. 73 75 72 72 72 at 66 psi 72 95 93 99 89 77 9 Annealed HDT 90° C., at 264 psi 107 90 83 78 79 at 66 psi o 17 116 104. O2 109 Rockwell Hardness, 99 109 09 109 109 97 102 R Scale

A control blend (100 parts by weight of the same PVC EXAMPLE I and no styrene-maleic anhydride copolymer) having the Another blend of this invention was made using “Dy Same amounts of the same other ingredients was also lark' DKB-290, a product of ARCO/Polymers, Inc., an made. The dynamic thermal stability (DTS) of these 45 unmodified styrene-maleic anhydride copolymer con blends was as follows: taining 18 percent by weight of maleic anhydride. The

Styrene-Maleic Anhydride Copolymer Used None (Control) DKB-134 DKB-134 DKB-290 DKB-332 DKB-350 DKB-28 DTS (minutes) 17.5 14 16 2.5 14 2.5 1 Equilibrium 790 900 890 970 1100 150 1090 Torque (m-g) Banbury drop 320 340 320 320 320 320 320 temperature F.

The- above- - blends werea injection molded on a New same formulation of ingredients as in Example I was Britain injection molding machine at the following con used. A control sample was also made. The properties ditions: of the blends are given in Table II. 60 TABLE I Zone 31O F. Physical Properties of Blend Zone 2 320 F. "Dwark Zone 3 330 F. a Nozzle 70% Control OKB-290 Injection Speed 5 turns off maximum 65 Specific Gravity 1.324 2O8 Shot Size 1.25-3 Tensile-Yield, psi 5730 6440 Hold Time 5 seconds Tensile Elastic Mod., 10 psi 333 365 Cooling Time 35 seconds Elongation, % 12.7 5 Mold Temperature, F. 100/100 Flexural Strength, psi 10.00 1 1,400 4,510,280 9 10 TABLE II-continued about 14 to about 20 weight percent of maleic anhy dride. Physical Properties of Bend 4. A composition of claim 1 wherein said admixture "Dylark" contains about 50 weight percent of (a) and about 50 Control DKB-290 weight percent of (b). Flexural Elastic Mod., 10 psi 322 378 Izod Impact. ft-lb/in. 5. A composition of claim 1 wherein (a) is polyvinyl inch bar 9.2 0.5 chloride. inch bar 16.1 0.5 6. A composition of claim 1 wherein (a) is polyvinyl Heat Deflection Temperature, chloride having a relative viscosity as measured at a C. 10 concentration of 1 gram per 100 grams of cyclohexa at 264 psi 65 73 at 66 psi 72 92 none at 25 C. falling within the range of about 1.50 to Heat Deflection Temperature, about 1.65. (annealed at 90° C.) 7. A composition of claim 1 wherein (a) is polyvinyl at 264 psi 72 OO chloride and (b) is a graft copolymer of a styrene and at 66 psi 76 2 15 maleic anhydride. Rockwell Hardness, R. Scale 99 09 8. A composition of claim 1 wherein (a) is polyvinyl Vicat Softening Point, C. w 15 Brabender Equilibrium Torque 780 890 chloride having a relative viscosity as measured at a (m-g) concentration of 1 gram per 100 grams of cyclohexa Brabender DTS, minutes 18 8 none at 25 C. falling within the range of about 1.50 to Spiral Flow, inches 8.5 19.75 20 about 1.65, and (b) is a graft copolymer of styrene and Screw Recovery Time, seconds 11 9 maleic anhydride in which the relative proportions thereof fall within the range of about 86 to 80 weight The most preferred compositions of this invention percent of styrene and about 14 to about 20 weight have the following properties: percent of maleic anhydride. An Izod impact strength (ASTM D256, Method A) of 25 9. A composition of claim 1 wherein said graft co at least 1.0 foot pound per inch, polymer contains up to 25 parts by weight of the rubber A heat deflection temperature (ASTM D 648) at 66 psi per 100 parts by weight of the copolymer. of at least 85 C., and 10. A polyblend composition comprising: A dynamic thermal stability of at least 10 minutes. A. from 35 to 60% by weight of polyvinylchloride This invention is susceptible to variation within the 30 B. from 65 to 40% by weight of a rubber-modified spirit and scope of the invention herein disclosed and copolymer of a vinylaromatic monomer, and unsat claimed. urated dicarboxylic acid anhydride and copoly We claim: merizable termonomer, wherein the relative 1. A thermoplastic composition which comprises in weight proportions of the monomers are about 70 intimate admixture: 35 to about 91% of the vinylaromatic monomer, about (a) a vinyl chloride polymer having a relative viscos 9 to 30% of the anhydride and 0 to 20% of the ity as measured at a concentration of 1 gram per termonomer; and wherein the monomers are poly 100 grams of cyclohexanone at 25°C. falling within merized in the presence of 5 to 25% of a rubber the range of about 1.50 to about 1.85; and having a glass transition temperature below 0°C.; (b) a rubber-modified graft copolymer of a vinyl 40 and aromatic compound and an ol.f3-unsaturated cyclic C. from about 5 to about 20% by weight of a compo anhydride in which the relative proportions of said sition comprising a graft copolymer of a monomer compound and said anhydride fall within the range selected from the group comprising methyl meth of about 91 to about 70 weight percent of said acrylate and acrylonitrile and a vinyl aromatic compound and about 9 to about 30 weight percent 45 monomer said copolymer being grafted onto a of said anhydride, and in which the graft copoly substrate rubber. mer contains up to 33 parts by weight of the rubber 11. A composition according to claim 10 in which the per 100 parts by weight of the copolymer; and termonomer in Component B is selected from the group (c) a tin-containing stabilizer and an impact modifier consisting of C1 to C2 alkyl acrylates and methacrylates for vinyl chloride polymers; 50 and unsaturated nitriles. with the proviso that said admixture contains 60 to 35 12. A composition according to claim 11 in which weight percent of (a) and 40 to 65 weight percent of (b) Component B is a rubber-modified styrene/maleic an and the further proviso that the blend has the following hydride/methyl methacrylate terpolymer. properties: 13. A composition according to claim 10 that incor (d) an Izod impact strength (ASTM D256, Method 55 porates about 10% by weight of Component C. A) of at least 0.5 foot pound per inch; 14. A composition according to claim 10 in which (e) a heat deflection temperature (ASTM D 648) at 66 Component C is a rubber-modified styrene/methyl psi of at least 75° C.; and methacrylate copolymer. (f) a dynamic thermal stability of at least 10 minutes. 15. A composition according to claim 10 in which 2. A composition of claim 1 wherein (b) is a graft 60 Component C is a rubber-modified styrene/acryloni copolymer of a styrene and maleic anhydride. trile copolymer. 3. A composition of claim 1 wherein (b) is a graft 16. A composition according to any one of claims 10 copolymer of a styrene and a maleic anhydride in which to 15 in which Component A represents from 40 to 55% the relative proportions thereof fall within the range of of the composition weight. about 86 to about 80 weight percent of styrene and 65