CA1065089A

CA1065089A - THERMOPLASTIC MOLDING COMPOSITIONS OF VINYL AROMATIC COMPOUND .alpha.(.beta.-UNSATURATED CYCLIC ANHYDRIDE COPOLYMERS

Info

Publication number: CA1065089A
Application number: CA230,751A
Authority: CA
Inventors: Visvaldis Abolins; Gim F. Lee (Jr.)
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1975-06-26
Filing date: 1975-06-26
Publication date: 1979-10-23

Abstract

ABSTRACT OF THE DISCLOSURE Novel thermoplastic molding compositions are disclosed which comprise a copolymer of vinyl aromatic compound with an .alpha. , .beta. -unsaturated cyclic anhydride and a hydrogenated A-B-A block copolymer of a block copolymer of the A'-B'-A' type or an acrylic graft polymerization copolymer with or without a polyphenylene ether resin.

Description

~065089 This invention relates to thermopla~tic molding compositions that are based on a copolymer of a vinyl aromatic compound with an ~ unsaturated cyclic anhydride and a hydrogenated, A-B-A block copolymer or a block copolymer of the A'-B'-A' type or an acrylic graft polymerization copolymer with or without a polyphenylene resin.
The term "polyphenylene ether resin" includes a family of polymers well known to those skilled in the art, they are made by a variety of catalytic and non-catalytic processes from the corresponding phenols or reactive derivatives thereof.
By way of illustration, cartain of the following polyphenylene ethers are discussed in Hay, U.S. Patents 3,306,874 and 3,306,875 issued February 28, 1967 and in Stamatoff, U.S. Patent 3,257,357 and 3,257,358 issued June 21, 1966. ~lso, the Bennett and Cooper U.S. patents 3,639,656 issued February 1, 1972, 3,642,699 issued February 15, 1972 and 3,661,848 issued May 9, 1972 describe processes for the preparation of polyphenylene ethers. In the Stamatoff patents, the polyphenylene ethers are produced by reacting the corresponding phenolate ion with an initiator, such as peroxy acid salt, an acid peroxide, a ~ ~ -hypohalite, and the like, in the presence of a complexing agent. Discloæures relating to non-catalytic proces6es, such as oxidation with lead dioxide, silver oxide, etc., are described in Price et al, U.S. patent 3,382,212 issued May 7, 1968.
The Cizek U.S. patent 3,383,435 issued May 14, 1968 discloses blends of polyphenylene ether resins and styrene resins. The thermoplastic compositions disclosed by Cizek - may include rubber-modified styrene resin, as well as crystal polystyrene. The Carmelite, Kramer and Lee, Jr. U.S. patent 3,787,532 issued January 22, 1974, also discloses polypheny- -lene ether containing compositions.
"

~065089 U.S. patent 3,660,531 - Shaw ,et al - issued May 2, 1972 discloses compositions of a polyphenylene ether styrene resin and a styrene-butadiene-styrene block copolymer. These ~mpositions have a major proportion of polyphenylene ether polymer.
There have been many attempts to upgrade the heat distortion temperature and the impact resistance of vinyl aromatic resins. One approach has been to provide copolymers of the vinyl aromatic compounds with ~ unsaturated cyclic anhydrides. In the case of styrene-maleic anhydride ` copolymers, a level of 20% of maleic anhydride increases the heat distortion temperature but the resulting material is very brittle.
Accordingly, it is a principla object to provide improved compositions of vinyl aromatic resins that have higher heat distortion temperatures and better impact strengths ; particularly as measured in terms of the Gardner impact tests.
According to the present invention, there is provided a composition that is useful in the manufacture of thermo-plastic molded articles. These thermoplastic molding compositions comprise:
(a) from 40-95 parts by weight, preferably from 40-80 parts by weight of a copolymer of a vinyl aromatic compound and an ~ , ~ -unsaturated cyclic anhydride;
(b) from 5-40 parts by weight, preferably 10-30 parts by weight of a block copolymer selected from the group consisting of:
i. hydrogenated block copolymers of the A-B-A type wherein prior to hydrogenation; A is a polymerized mono-alkenyl aromatic hydrocarbon block; B is a polymerized con-jugated diene hydrocarbon block; the blocks A constituting

2-50 weight percent of the copolymer and the unsaturation of " .

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~o6S089 block B having been reduced by hydrogenation.
ii. block copolymers of the A'-B'-A' type wherein A
iæ a polymerized mono-alkenyl aromatic hydrocarbon block and B ' is a polymerized conjugated diene block, the block B ' being of higher molecular weight than that of the combined molecular weight of terminal blocks A';
iii. emulsion graft polymerization product of an acrylic monomer alone or in admixture with a styrene monomer on a rubbery diene homopolymer of styrene-diene copolymer backbone;
and iv. mixtures of the foregoing; and (c) from 0-50 parts by weight, preferably 0-40 parts by weight of a polyphenylene ether resin.
The preferred compositions will include 5-20 parts by weight of the polyphenylene ether resin. The PPO containing compositions will have a ratio of the copolymer of the vinyl compound and the ~ , ~ -unsaturated cyclic anhydride to polyphenylene ether resin that is greater than one. The polyphenylene ether resins are preferably of the formula: ;~
` Q

~
n ; wherein the oxygen ether atom of one unit is connected to the benzene nucleus of the next adjoining unit, n is a positive integer and is at least 50, and each Q is a monovalent sub-stituent selected from the group consisting of hydrogen, halogen, hydrocaxbon radicals, halohydrocarbon radicals having at least two carbon atoms between the halogen atom and the phenyl nucleus, hydrocarbonoxy radicals, and halohydrocarbonoxy ', , .~, :

~065089 radicals havinq at least two carbon atoms between the halogen atom and phenyl nucleus, said radicals being free of a tertiary alpha-carbon atom. The preparation of polyphenylene ether resins corresponding to the above formula is described in the above-mentioned patents of Hay and Stamatoff. Especially preferred polyphenylene ether resins for purposes of the present invention are those having alkyl substitution in the two positions ortho to the oxygen ether atom -- i.e., where each Q is alkyl, most preferably, having from 1 to 4 carbon atoms. The most preferred polyphenylene ether resin for purposes of the present invention is poly(2,6-dimenthyl-1,4-phenylene) ether (each Q is methyl)~
The copolymers of the vinyl aromatic compounds and the ~ , ~ -unsaturated cyclic anhydride are well known and are described in the literature. The vinyl aromatic component may be derived from compounds of the formula:

CRl = CHR2 R5 ~ R3 -~ ~ ~ R4 , R6 ~
wherein Rl and R2 are selected from the group consisting of lower alkyl or alkenyl groups of from 1 to 6 carbon atoms and hydrogen; R3 and R4 are selected from the group consisting of chloro, bromo, hydrogen and lower alkyl of from 1 to 6 carbon atoms; R5 and R6 are selected from the group consisting of hydrogen and lower alkyl and alkenyl groups of from 1 to 6 -i carbon atoms or R5 and R6 may be concatenated together with hydrocarbyl groups to form a naphthyl group. These compounds are free of any substituent that has a tertiary carbon atom.
Styrene is the preferred vinyl aromatic compound. The .

unsaturated cyclic anhydrides include maleic anhydride, citraconic anhydride, itaconic anhydride, aconitic anhydride and the like. The preferred ~ unsaturated cyclic anhy-dride is maleic anhydride.
These polymers may comprise 40 to 1 mole percent of the ~ , ~ -unsaturated cyclic anhydride and from 60 to ~9 mole percent of a vinyl aromatic compound. The preferred polymers will contain about 25-5 mole percent of the ~ , -unsaturated cyclic anhydride and 75-95 mole percent of the vinyl aromatic compound. The preparation of these copoly-mers are described in U.S. patent 2,971,939 - Baer - issued February 14, 1961; U.S. Patent 3,336,267 - Zimmerman, et al issued August 15, 1967; and U.S. Patent 2,769,804 - Hanson -issued November 6, 1956.
With respect to the hydrogenated block copolymers of the A-B-A type, they are made by means known in the art ~- and they are commercially available.
These materials are described in U,S. Patent . .. . .

3,421,323 - Bennett Jr. - issued January 14, 1969.
Prior to hydrogenation, the end blocks of these copolymers comprise homopolymers or copolymers preferably prepared from alkenyl aromatic hydrocarbons and particularly vinyl aromatic hydrocarbons wherein the aromatic moiety may be either monocyclic or polycyclic. Typical monomers include styrene, alpha methyl styrene, vinyl xylene, ethyl vinyl xylene, vinyl naphthalene and the like or mixtures thereofO
The end blocks may be the same or different. The center block may be derived from, for example, polyisoprene or poly-butadiene.
The ratio of the copolymers and the average molecular weights can vary broadly although the molecular weight of center block should be greater than that of the .. . . .
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~065~89 combined terminal blocks. It is preferred to form terminal blocks A having average molecular weights of 4,000-115,000 and center block B e.g., a polybutadiene block with an average molecular weight of 20,000 - 450,000. Still more preferably, the terminal blocks have average molecular weights of 8,000 -60,000 while the polybutadiene polymer blocks has an average molecular weight between 50,000 and 300,000. The terminal blocks will preferably comprise 2-50% by weight, or more preferably, 5-30% by weight of the total block polymer. The preferred copolymers will be those formed from a copolymer having a polybutadiene center block wherein 35-55%, or more preferably, 40-50% of the butadiene carbon atoms are vinyl side chains.
The hydrogenated copolymers may have the average unsaturated reduced to from 95 to 5% of the original value.
It is preferred to have the unsaturation of the center block B reduced to 10%, or more preferably, 5% of its original value~
The block copolymers are formed by tenchiques well - known to those skilled in the art. Hydrogenation may be conducted utilizing a variety of hydrogenation catalysts such as nickel or kieselguhr, Raney nickel, copper chromate, molybdenum sulfide and finely divided platinum or other noble metals on a low surface area carrier.
Hydrogenation may be ~ nducted at any desired temperature or pressure, from atmospheric to 300 p.s.i.g.
the usual range being between 100 and 1000 p.s.i.g. at temperatures from 750F to 600 F for times between 0.1 to 24 hours, preferably from 0.2-8 hours.
Hydrogenated block copolymers such as Kraton G-GXT-0650, Kraton G-GXT-0772 and Kraton G-GXT-0782 from Shell Chemical Compahy, Polymers Division have been found useable according to this invention.
With respect to the A'-B'-A' block copolymers, .
. . , ': .- - . , 10651~89 they may be made by means well known in the art and are also available commercially from a number of sources.
Block copolymers of vinyl aromatic compounds and conjugated dienes are described in Kennedy, et al Editor, Polymer Chemistry of Synthetic Elastomers, Interscience, Vol. 23, Part II, 1969, pages 553-559. In general, they will be of the A-s-A' type in which the center and end blocks can vary. In the compositions of this invention, the central block B, will preferably be that of a conjugated diene, e.g,, butadiene; isoprene; 1,3-pentadiene: 2,3-dimethyl-butadiene, and the like or mixtures of the foregoing. The terminal blocks A and A'~ will be the same or different, but will always be derived from a vinyl aromatic compound, e.g., styrene, ~-methyl styrene, vinyl toluene, vinyl xylene, vinyl naphthalene, or mixtures of any of the foregoing. In the most preferred compositions, the block copolymer will have terminal . .
; blocks A and A' comprised of polystyrene and center block B
comprised o$ polybutadiene.
The ratio of the comonomers can vary broadly, so long as the molecular weight center block is greater than that of the combined terminal blocks. Preferably, with the ~ -above limitation, the molecular weight of the terminal blocks each will range from about 2000 to about 100,000 while that of the center block will range from about 25,000 to about 1,000,000.
The block copolymers are made by an organometallic initiated polymerization process using, for example sodium or lithium metal an organic derivative thereof. The diene monomers can be polymerized with a monofunctional or di-functional initiator, as is described in Kennedy et al, mentioned above.
In one process, the block copolymer is prepared by ... . . ..
,-., .' .' ...", ', ' ., ~, ,.

106S~)89 dissolving the conjugated diene, e.g., butadiene, in an aro-matic hydrocarbon solvent, e.g., xylene, toluene, etc., and adding 0.3 to 7.5 millimoles/100 parts of monomer of an organodilithium initiator, e.g., dilithiobutane, dilithio-stilbene, etc. Polymerization of the diene is completed and then the vinyl aromatic compound is added and polymerization of this is completed to form the block copolymer. The product is precipitated and deactivated, e.g., with alcohol, such as ethanol or isopropanol and purified by redissolving in hydrocarbon and reprecipitating with alcohol.
Full descriptive details of such a process are given in Zelinski, U.S. patent 3,251,905 issued May 17, 1966.
- In another process, the block copolymer is built up sequentially using, e.g., a secondary or tertiary alkyl lithium compound at about 100-2000 parts per million based on the total weight of the monomers and a polymerization temperature in the range 20-65C. For example, styrene is dissolved in cyclohexane at 32C. and treated with 5530 parts per million of secondary butyl lithium. After polymerization ~ 20 is complete, isoprene is injected and polymerization is `~ continued at 55-57C. Finally styrene is added and the third block is polymerized. The product can be recovered as described above. Full descriptive details of such a process are given in Holden et al, U.S. patent 3,231,635- issued January 25, 1966. These materials are commercially available as Kraton resins.
The graft polymerization product of an a¢rylic monomer and a diene rubber preferably comprises (1) from ~ about 20-80% by weight of a backbone polymer of the units of i 30 butadiene or butadiene and styrene, wherein the butadiene units are present in quantities of at least 40% by weight of the backbone polymer, (2) 80-20% by weight of an acrylic monomer graft polymerlzed to (l); said acrylic monomer units being selected from the group consisting of lower alkyl meth-acrylates, alicyclic methacrylates and alkyl acrylates, and (3) 0 to 60% by weight of a styrene monomer graft polymerized to (1) or (2); sequ~ntially or simultaneously with the polymerization of (2).
The graft polymerization product of an acrylic monomer alone or with styrene monomer and the rubbery diene polymer or copolymer may be prepared by known techniques, typically by emulsion polymerization. They may be formed from a styrens-butadiene copolymer latex and a monomeric material such as methyl methacrylate alone or with another compound having a single vinylidene group copolymerizable therewith, e.g., styrene~ For example, in the preparation of a re-presentative material, 85-65 parts by weight of monomeric methyl methacrylate or monomeric methyl methacrylate to the extent of at least 55% and preferably as much as 75% by weight in admixture with another monomer which copolymerizes therewith, such as ethyl acrylate, acrylonitrile, vinylidene chloride, styrene, and similar ungaturated compounds containing a single vinylidene group, is added to 15-35 part~ by weight of solids in a styrene-butadiene copolymer latex. The co polymer solids in the latex comprise about 10-50% by weight of styrene and about 90-50% by weight of butadiene and the molecular weight thereof is within the range of about 25,000 to l,S00,000. The copolymer latex of solids in water contains a dispersing agent such as sodium oleate or the like to maintain the copolymer in emulsion. Interpolymerization of the monomer or monomeric mixture with the copolymer solids emulsified in water is brought about in the presence of a free-radical generating catalyst and a polymerization - regulator which serves as a chain transfer agent, at a 106508~
temperature of the order of 15C to 80C . Coagulation of the interpolymerized product is then effected with a calcium chloride solution, for instance, whereupon it is filtered, washed and dri~d. Other graft copolymers and differing from the above only in the ratio of monomeric material solely or preponderantly of methyl methacrylate to the butadiene-styrene copolymer latex in the presence of which it is poly-merized extends from 85-25 parts by weight of the former to 15-75 parts by weight of the latter. These materlals may extend in physical properties from relatively rigid compositions to rubbery compositions. A preferred commercially available material is Acryloid KM 611 which is sold by Rohm ~ Haas.
Also, U.S. patent 2,943,074 - Feuer - issued June 28, 1960 and U.S. patent 2,857,360 - Feuer-- issued October 21, 1958, contain additional information as to the preparation of these materials. A preferred material is described in U.S. patent 2,943,074, column 4, preparation "D" and converted to emulsified polymer "B" as described therein.
The compositions of this invention will preferably include deom 40-80 parts of the copolymer of a vinyl aromatic compound and a ~ , ~ -unsaturated cyclic anhydride, and most preferably from 60-75 parts by weight of this material. The block copolymer of the A-B-A type or A'-B'~A' type, or the -- acrylic graft polymerization product, will preferably be present at from 10-40 parts by weight and most preferably at 20-30 parts by weight. If employed, the polyphenylene ether resins are preferably present at a level of from 1-40 parts by weight and preferably at a level of from 5-30 parts by weight.
~he compositions of the invention may also include reinforcing fillers, such as aluminum, iron or nickel, and the like, and non-metals, such as carbon filaments, silicates, such as acicular calcium silicate, asbestos, titanium dioxide, ~ . '' ' ' ~065089 potassium titanate and titanate whiskers, glass flakes and fibers. It is also to be understood that, unless the filler adds to the strength and stiffness of the composition, it is only a filler and not a reinforcing filler,as contemplated herein. In particular, the reinforcing fillers increase the flexural strength, the flexural modulus, the tensile strength and the heat distortion temperature.
Although it is only necessary to have at least a reinforcing amount of the reinforcement present, in general, the combination of components (a) and tb) will comprise from about 10 to about 90 parts by weight and the filler will com-prise from a~out 10 to about 90 parts by weight of the total composition.
In particular, the preferred reinforcing fillers -- are of glass and it is preferred to use fibrous glass filaments comprised of line-aluminum borosilicate glass that is relatively soda free. This is known as "E" glass. However, other glasses are useful where electrical properties are not so important, e.g., the low soda glass known as "C" glass. The filaments are made b~y standard processes, e.g., by steam or air blowing, flame blowing and mechanical pulling. The pre-ferred filaments for plastics reinforcement are made by mechanical pulling. The filament diameters range from about - 0.000112 to 0.00075 inch, but this is not critical to the present invention.
In general, best properties will be obtained if the sized filamentous glass reinforcement comprises from about 1 to about 80% by weight based on the combined weight of glass '`A and polymers and preferably from about 10 to about 50% by weight. Especially preferably the glass will comprise from about 10 to about 40% by weight based on the combined weight of glass and resin. Generally, for direct molding use, up to .

~()6S~9 about 60% of glass can be present without causing flow problems.
However, it is useful also to prepare the compositions con-taining substantially greater quantities, e.g., up to 70-80%
by weight of glass. These concentrates can then be custom blended with blends of resins that are not glass reinforced to provide any desired glass content of a lower value.
The length of glass filaments and whether or not they are bundled into fibers and the fibers bundled in turn to yarns, ropes or rovings, or woven into mates, and the like, are also not critical to the invention. However, in pre-paring the present compositions it is convenient to use the filamentous glass in form of chopped strands of from about 1/8" to about 1" long, preferably less than 1/4" long. In articles molded from the compositions, on the other hand, even shorter lengths will be encountered because, during compounding, considerable fragmentation will occur. This is desirable, however, because the best properties are exhibited by thermo-plastic injection molded articles in which the ~ilament lengths lie between about 0.000005" and 0.125 (1/8").
It is a preferred feature of this invention also to provide flame retardant thermoplastic compositions of vinyl aro~atic~ -unsaturated cyclic anhydrides as defined above by modifying said compositions to include a flame-retardant additive in a minor proportion but in an amount at least sufficient to render the composition non-burning or self-extinguishing.
Particular glame retardants which may be used are well known and are described in the literature.
The compositions may be prepared by tumbling the components, extruding the mixed powders into a continuous strand, chopping the ~trands into pellets and thereafter molding the pellets into the desired shape. These techniques are well known to those skilled in this are and are not a critical ' ~ ' ' 1~65~89 feature of the invention.
The present invention is further illustrated in the following examples which are set forth as further descrip-tions of the invention, but are not to be construed as limiting the invention thereto.
EæAMPLE I
The compositions listed in Table 1 were prepared by compounding the components on a 28 mm. W.P. extruder at a feed temperature of 550F, a rear temperature of 570F, a 10front temperature of 580F, and a die temperature of 590F.
The materials were molded on a 3 oz. ~ewbury injection molding machine at 400F cylinder temperature and 130F mold temperature. The cycle time was 35 seconds.

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106S~89 The compositions described in Table 1 were evaluated for physical properties and the results are reported in Table 2.

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1~6~089 An analysis of this Table shows that the compositions of this invention have good impact strengths and relatively high heat dis~ortion temperature.
Other compositions may be prepared by using the following materials:
A. styrene-maleic anhydride copolymer prepared accoding to Example II, run 10 of U.S. 3,336,267.
B. A-B-A block copolymer prepared according to run B of U.S. 3,431,323 - Jones - issued March 4, 1969.
c. A'-B'-A' block copolymer of ~tyrene-butadiene-styrene prepared according to Example II of U.S. 3,265,765 -Holden - issued August 9, 1966.
D. emulsion graft polymerization product of an acrylic monomer and a rubbery diene copolymer as prepared in U,S. 2,843,074, column 4, emulsified polymer "B" .
-~ EXAMPLE II
~;' The following compositions were prepared using procedures analogous to those employed in Example I:
SamPle No. 19 20 21 _22 23 24 Components (~arts bv weiaht) I poly~2,6-dimethyl-1,4-Ehenylene) ether (PPO'~General Elec-tric Co.) -- 10 -- 10 -- 10 II A-B-A copolymera 70 60 -- -- -- --~;~ III A'-B'-A- copolymerb -- -- -- -- 30 30 - IV emulsion graft poly-merization product of an acrylic monomer on a rubbery diene poly-merC -- -- 25 25 -- -- -V styrene-maleic 3nhy-dride copolymer 30 30 75 65 70 60 a Kraton GXT-0650, Shell Chemical Co.
b Kraton 4119, Shell Chemical Co.
c Acryloid ~ 611 Rohm & Haas.
d Dylark 232, Sinclair Koppers; crystal grade.

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1065~89 The compositions of Example II were evaluated for physical properties and the results are reported in Table 3.

~otched Izod Imp.
(ft.lb./in.n) 1.3 7.70.40.4 2.4 5.5 H8at Distortion Temp. __ __ __ _ Gardner Impact (in./lb.) 63 155 10 10 65 81 - 10 Tensile Strength (p8i)5700 61008100850040004700 Obviously other modifications and variations of the present invention are possible in the light of the above teachings. It is, therefore, to be understood that changes may be made in the particular embodiments of the invention described which are within the full intended scope of the invcntion as dofined by the appended cl~ims.

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Claims

The embodiments of the invention in which an exclu-sive property or privilege is claimed are defined as follows:

1. A thermoplastic molding composition which comprises:
(a) from 40-95 parts by weight of a copolymer of a vinyl aromatic compound and an .alpha.,.beta.-unsaturated cyclic anhydride;
(b) from 10-50 parts by weight of a block copolymer selected from the group consisting of:
i. hydrogenated block copolymers of the A-B-A type wherein prior to hydrogenation; A is a polymerized mono-alkenyl aromatic hydrocarbon block; B is a polymerized conjugated diene hydrocarbon block; the block A constituting 2-50 weight percent of the copolymer;
ii. emulsion graft polymerization product of an acrylic monomer alone or in admixture with a styrene monomer on a rubbery diene homopolymer or styrene-diene copolymer back-bone;
iii. mixtures of the foregoing;
(c) from 0-50 parts by weight of a polyphenylene ether resin.

2. A composition as defined in claim 1 wherein said composition includes from 5-20 parts by weight of a polyphenylene ether of the formula:

wherein the oxygen ether atom of one unit is connected to the benzene nucleus of the next adjoining unit; n is an integer of at least 50; and each Q is a monovalent substituent selected from hydrogen, halogen, hydrocarbon radicals, halohydrocarbon radicals having at least two carbon atoms between the halogen atom and the phenyl nucleus.

3. A composition as defined in claim 1 wherein said composition includes a hydrogenated block copolymer of the A-B-A
type wherein prior to hydrogenation:
i. A is a polymerized mono-alkenyl aromatic hydrocarbon block having an average molecular weight of about 4,000-115,000;
ii. B is a polymerized conjugated diene hydrocarbon block having an average molecular weight of about 20,000-450,000;
iii. the blocks A constituting 2-33 weight percent of the copolymer;
iv. 35-55% of the conjugated diene carbon atoms in block B being vinyl side chains;
v. and the unsaturation of block B having been reduced to less than 10% of the original unsaturation.

4. A composition as defined in claim 1 wherein the copolymer of a vinyl aromatic compound and an unsaturated cyclic anhydride is based on a vinyl aromatic compound of the formula:

wherein R1 and R2 are selected from the group consisting of lower alkyl or alkenyl groups of from 1 to 6 carbon atoms and hydrogen; R3 and R4 are selected from the group consisting of chloro, bromo, hydrogen and lower alkyl of from 1 to 6 carbon atoms; R5 and R6 are selected from the group consisting of hydrogen and lower alkyl and alkenyl groups of from 1 to 5 carbon atoms or R5 and R6 may be concatenated together with hydrocarbyl groups to form a naphthyl group, said compounds being free of any substituent that has a tertiary carbon atom.

5. A composition as defined in claim 1, 2 or 3 where said copolymer of a vinyl aromatic compound and an .alpha.,.beta.-unsaturated cyclic anhydride comprises from 40 to 1 mole percent of the .alpha.,.beta.-unsaturated cyclic anhydride and from 60 to 99 mole percent of a vinyl aromatic compound.

6. A composition as defined in claim 1, 2 or 3 which contains from 5-30 parts by weight of said poly(2,6-dimethyl-1,4-phenylene) ether; and from 40-80 parts by weight of a copolymer of styrene-maleic anhydride.

7. A composition as defined in claim 4 which contains from 5-30 parts by weight of poly(2,6-dimethyl-1,4-phenylene) ether and from 40-80 parts by weight of a copolymer of styrene-maleic anhydride.

8. A composition as defined in claim 1 which contains 0% of the polyphenylene ether component.

9. A composition as defined in claim 8 which contains a hydrogenated block copolymer of the A-B-A type.

10. A thermoplastic molding composition which comprises from 60-75 parts by weight of a copolymer of styrene-maleic acid anhydride, from 10-40 parts by weight of a hydro-genated block copolymer of the A-B-A type wherein prior to hydrogenation:
i. A is a polymerized mono-alkenyl aromatic hydro-carbon block;
ii. B is a polymerized conjugated diene hydrocarbon block;
iii. the blocks A constituting 2-33 weight percent of the copolymer;
iv. and the unsaturation of block B having been reduced to less than 10% of the original unsaturation; and from 5-30 parts by weight of a polyphenylene ether resin.

11. A thermoplastic molding composition as defined in claim 1, 2 or 3 wherein component (a) is a copolymer of styrene-maleic acid anhydride, component (b) is of type (ii) and wherein components a, b and c are present in the range 60-75 parts, 10-40 parts and 5-30 parts by weight respectively.

12. A composition as defined in claim 8 which contains an emulsion graft copolymer comprising (1) from 20-80%
by weight of a backbone polymer of the units of butadiene or butadiene and styrene, wherein the butadiene units are present in quantities of at least 40% by weight of the backbone polymer, (2) 80-20% by weight of an acrylic monomer chosen from the group consisting of lower alkyl methacrylates, alicyclic methacrylates and alkyl acrylates, graft polymerized to (1) and (3) 0 to 60% by weight of a styrene monomer graft poly-merized to (1) sequentially before the polymerization of (2).