RELATED COPENDING APPLICATIONS

This application is related to copending applica¬ tion S.N. 619,433, assigned to the same assignee as the present invention.

BACKGROUND OF THE INVENTION

This invention relates to novel polyphenylene ether blends and, more particularly, to polymer blends comprising polyphenylene ether in combination with poly¬ styrene and an acrylic resin modified polyolefin which provide molded articles that do not suffer from delamina- tion.

The polyphenylene ethers are known and described in numerous publications including Hay, U.S. 3,306,874 and 3,306,875. The high molecular weight polyphenylene ethers are high performance engineering thermoplastics possessing relatively high viscosities and softening points and are useful for many commercial applications including formation of films, fibers and molded articles. It is known in the art that properties of the polyphenylene ether resins can be materially altered by blending them with other resins. For example, in commonly assigned patent U.S. 3,383,435, Cizek discloses that polyphenylene ether resins and polystyrene resins are combinable in all proportions and result in compositions having improved properties over those of either of the components.

To enhance the solvent resistance of these poly¬ phenylene ether-styrene resin blends, a more solvent resis¬ tant component is typically added. The addition of polyol¬ efins. to enhance the solvent resistance of these blends has been disclosed in commonly assigned patent U.S. 3,361,851. Acrylic resin modified polyolefins are often preferred for their ^* superior solvent resistance. Commonly assigned patents U.S. 3,794,606, 3,833,687, 3,833,688 and 4,020,124 describe acrylic resin modified polyolefins which provide outstanding solvent resistance to polyphenylene ether blends and- polyphenylene ether/polystyrene blends.

While these acrylic resin modified polyolefins have provided the desired solvent resistance, there still remains room for improvement. These blends often suffer from. delamination when processed into finished articles, which is believed to be caused by a phase separation of the polyolefins within the blend. Finished articles which suffer from delamination exhibit diminished impact resis¬ tance.. In related copending application S.N. 619,433, a matrix- compatibilizer having aromatic moieties is introduced into the polyphenylene ether/polystyrene blends to reduce phase separation of the elastomers described therein.

It has been discovered that neutralization of the acid functional groups on these acrylic modified polyolefins during melt blending enhances their compatibility with polyphenylene ether/polystyrene blends to the extent that a matrix compatibilizer is not needed.

SUMMARY OF THE INVENTION

A thermoplastic composition is provided which comprises:

(a) a polyphenylene ether resin in combination with a polystyrene resin,

(b) an amount, effective to increase solvent resis¬ tance, of a polyolefin polymer substantially free of aromat- ic moieties functionalized with substituents selected from the class consisting of carboxylic acid, lower alkyl esters of carboxylic acid and anhydrides of carboxylic acid,

(c) an amount, effective to compatibilize component (b) with component (a), of a neutralizing agent selected from the group consisting of metal salts of fatty acids and metal oxide/fatty acid combinations.

Preferred compositions will be those in which the polyphenylene ether comprises at least 1% by weight of the total resinous components in the composition. It is to be understood, however, that the present , compositions can also include conventional amounts of additives for processibility, flame retardancy, stability and the like.

An object of the present invention to provide solvent resistant blends of polyphenylene ether/polystyrene resins which do not suffer from delamination. A further object of the present invention is to provide compatibilized polyphenylene ether/polystyrene/acrylic resin modified polyolefin blends which do not utilize a polymer matrix compatibilizer. It is another object of the present inven¬ tion to provide solvent resistant blends of polyphenylene ether, polystyrene and acrylic resin modified polyolefin with improved impact strength. Other objects will be apparent from the detailed description herein.

DETAILED DESCRIPTION OF THE INVENTION

The polyphenylene ethers (also known as

polyphenylene oxides) used in the present invention are a well known class of polymers widely used in the industry. Since their discovery, they have given rise to numerous variations and modifications but still may, as a class, be generally characterized by the presence of aryleneoxy structural units. The present invention includes all of said variations and modifications, including but not limited to those described hereinafter.

The polyphenylene ethers generally comprise structural units having formula I below:

In each of said units independently, each Q is independent¬ ly hydrogen, halogen, primary or secondary lower alkyl (i.e. alkyl containing up to 7 carbon atoms), phenyl, haloalkyl or aminoalkyl wherein at least 2 carbon atoms separate the halogen or nitrogen atom from the benzene ring, hydrocar- bonoxy, or halohydrocarbonoxy wherein at least 2 carbon

2 atoms separate the halogen and oxygen atoms; and each Q is independently hydrogen, halogen, primary or secondary lower alkyl, phenyl, haloalkyl, hydrocarbonoxy or halohydrocarbon¬ oxy as defined for Q . Examples of suitable primary lower alkyl groups are methyl, ethyl, n-propyl, n-butyl, isobutyl, n-amyl, isoamyl, 2-methylbutyl, n-hexyl, 2,3-dimethylbutyl, 2,-3-or 4-methylpentyl and the corresponding heptyl groups. Examples of secondary lower alkyl groups are isopropyl, sec-butyl and 3-pentyl. Preferably, any alkyl radicals are straight chained rather than branched. Most often each Q is alkyl or phenyl, especially alkyl groups of 1 to 4 carbon

2 atoms and each is hydrogen. The most preferred polyphen¬ ylene ether resin for purposes of the present invention is ppoollyy--22--6-dimethyl-l,4-phenylene(ether) , wherein each Q is methyl, Suitable polyphenylene ethers are disclosed in a large number of patents. The following are illustrative but not limiting:

3,226,361 3,330,806 3,929,930 4,234,706

3,234,183 3,390,125 4,028,341 4,334,050 3,257,357 3,431,238 4,054,533 4,340,696

3,257,358 3,432,466 4,092,294 4,345,050

3,262,892 3,546,174 4,097,556 4,345,051

3,262,911 3,700,630 4,140,675 4,374,959

3,268,478 3,703,564 4,158,728 4,377,662 3,306,874 3,733,307 4,207,406 4,477,649

3,306,875 3,875,256 4,221,881 4,477,651

3,318,959 3,914,266 4,226,951 4,482,697

4,517,341.

Both homopolymers and copolymers are included. Suitable copolymers include random copolymers containing for example, 2, 6-dimethyl-l,4-phenylene ether units in combina¬ tion with 2,3,6-trimethyl-l,4-phenylene ether units, many of which are disclosed in various Hay patents. Also contem¬ plated are graft copolymers, including those prepared by grafting onto polyphenylene ether chain such vinyl monomers as acrylonitrile and vinyl aromatic compounds, for example, styrene, and by grafting other polymers such as polystyrenes and elastomers. Other suitable polymers are the coupled polyphenylene ethers in which the coupling agent is reacted with the hydroxy groups of two polyphenylene ether chains to increase the molecular weight of the polymer. Illustrative

coupling agents are low molecular weight polycarbonates, quinones, heterocycles, formals and phosphoryl groups.

The polyphenylene ether generally has a molecular weight (number average, as determined by gel permeation 5 chromatography whenever used herein) within the range of about 5,000 to 40,000; its intrinsic viscosity is most often in the range of 0.45-0.5 dl./g., as measured in chloroform at 25°C.

The polyphenylene ethers may be prepared by known 10 methods, typically by the oxidative coupling of at least one corresponding monohydroxy aromatic compound as described in the patents of Hay, referenced above. A particularly useful and readily available monohydroxy aromatic compound is

2',6-xylenol (wherein each Q 2 is hydrogen and each 1 is

15 methyl), whereupon the polymer may be characterized as a poly(2,6-dimethyl-l,4-phenylene ether) .

Any of the various catalyst systems known in the art to be useful for the preparation of polyphenylene ethers can be used in the preparing those employed in this inven-

20 tion. For the most part, they contain at least one heavy metal compound such as copper, manganese or cobalt compound usually in combination with various other materials.

A first class of preferred catalyst systems consists of those containing copper. Such catalysts are

25. disclosed, for example, in the aforementioned U.S. Patents 3 ^* .396,874, 3,306,875, 3,914,266 and 4,028,341. They are usually combinations of cupric and cupric ions, halide (i.e., chloride, bromide or iodide) ions and at least one amine.

30- Manganese-containing systems constitute a second preferred class of catalysts. They are generally alkaline systems containing divalent manganese and such ions as halide, alkoxide or phenoxide. Most often, the manganese is

present as a complex with one or more complexing and/or chelating agents such as dialkyl amines, alkanol amines, alkylene diamines, o-hydroxy aromatic aldehydes, o-hydroxy azocompounds, ω-hydroxyoximes (monomeric and polymeric) , o-hydroxyaryloximes and β-diketones. Also useful are cobalt-containing catalyst systems.

The following additional patents disclose manga¬ nese and cobalt-containing catalyst systems for polypheny¬ lene ether preparation:

3,956,242 4,083,828 4,184,034

3,962,181 4,093,596 4,315,086

3,965,069 4,093,597 4,335,233

3,972,851 4,093,598 4,385,168

4,058,504 4,102,865 4,075,174 4,110,312

Commercially prepared polyphenylene ethers are known to have at least one of the end groups shown in formulas II and III below

wherein 2 1 and 2 are as previously defined; each R1 is independently hydrogen or alkyl, with the proviso that the total number of carbons in both R radicals is 6 or less;

2 and each R is independently hydrogen or a primary alkyl radical of from 1 to 6 carbon atoms. Preferably, each R is

2 hydrogen and R is alkyl, especially methyl or n-butyl. In

many polyphenylene ethers obtained under the conditions described above, a substantial proportion of the polymer molecules, typically constituting as much as about 90% by weight of. the polymer, contain end groups having one or frequently both of formulas II and III. The benefits obtained from this invention are independent of the end groups- which appear on the polyphenylene ethers. Improved resistance to delamination is obtained with all the polyphen¬ ylene ethers. ^' As- is noted above, the polyphenylene ether can be combined, with a polystyrene and most preferably, a rubber modified high impact polystyrene resin. As disclosed in the above mentioned Cizek patent, the styrene resin most combin- able. with the polyphenylene ether resin is one having at least 25% by weight polymer units derived from the vinyl aromatic monomer having the formula:

where R is hydrogen, alkyl or alkenyl of from 1 to 4 carbon atoms, or halogen; Z is a member selected from the class consisting of vinyl, chlorine, bromine, hydrogen or alkyl of ^' from 1 to 4 carbon atoms and p is from 0 to 5. These polystyrene resins will typically exhibit a number average molecular weight of about 50,000 to 250,000. For the preferred styrene resins, R is hydrogen and p is 0. Such compositions will comprise from 99 to 1% by weight of the ^" polystyrene resin.

Examples of suitable polystyrene resins include the homopolymers of polystyrene and poly o-methyl styrene

and rubber modified, high-impact polystyrene resins. Examples of rubber modified, high-impact polystyrene resins include styrene acrylonitrile copolymers, styrene butadiene copolymers, styrene-acrylonitrile-butadiene copolymers, styrene-maleic anhydride copolymers, styrene-ethyl vinyl benzene copolymers, styrene-divinyl benzene copolymers, styrene-butadiene block copolymers, styrene-butadiene- styrene block copolymers, styrene-butadiene-maleic anhydride block copolymers and styrene-tertbutyl copolymers. For the compositions of this invention, it is preferable to maintain the use of halogenated styrene resins at a minimum. There¬ fore, only minor portions, e.g., less than about 10% weight percent of the total resinous components are acceptable.

The preferred styrene resin, for purposes of this invention, is one comprising a rubber modified polystyrene. ^• This modified polystyrene is obtained by blending or graft¬ ing from 3 to 30 percent by weight of a polybutadiene or a rubbery copolymer, e.g., of about 70% butadiene and 30% styrene. Although the un-modified polystyrene, e.g., crystal polystyrene, provides superior solvent resistance, the improvement in impact strength is not nearly so marked unless the styrene resin is rubber modified.

The functionalized polyolefins utilized in this invention have a polymer backbone which preferably consists entirely of carbon atoms, i.e. are preferably free of oxygen and other hydrolyzable linkages, such as ether and carbonate linkages. In addition, these functionalized polymers are substantially free of aromatic moieties. Therefore, the polymer backbones are primarily are aliphatic saturated and unsaturated carbon atoms. Although functionalized polyol¬ efins having aromatic moieties will provide suitable compo¬ sitions, it is an object of this invention to avoid their use. The term "polyolefin" is intended to include the lower

molecular weight, low T elastomers, as described in Ency¬ clopedia of Polymer Science and Technology, Vol. 5, (1966), pp. 406-482, and the rigid high molecular weight, high T olefin polymers, as described in Encyclopedia of Polymer 5 Science and Technology, Vol. 9, (1966), pp. 440-460, these d sc-Losures being incorporated by reference herein. Exam¬ ples, o__T suitable elastomers include synthetic diene rubbers such- as- polybutadiene and polyisoprene, butyl rubbers, polyisobutene rubbers, ethylene-propylene rubbers, ethy-

10. lene-propylene-diene rubbers wherein the diene is non-con¬ jugated. (EPDM rubbers), chloroprene rubbers, and others known- to the art. The molecular weights of these rubber backbones, without being functionalized, are typically about 10,000 ^" to 250,000 and most often about 20,000 to 100,000.

15 Suitable rigid olefin polymer backbones of a high

T. incrlude polyisobutene, poly(l-butene) , poly(l-pentene) , poly{3-methyl-l-butene) , polyethylene, polypropylene, polydecene, poly(l-octadecene) , and polyvinyl chloride. The molecular weights of these polymer backbones, before func-

20 tionalization, are typically about 50,000 to about ι;000,000.

The functional groups which may appear on the polymer backbones are carboxylic acids, lower alkyl esters of: carboxylic acids and anhydrides of carboxylic acids.

25 Suitable polyolefins with carboxylic acid func¬ tionality, include acrylic resin modified polyolefins. These modified polyolefins comprise graft, random and block copolymers obtained by polymerization of acrylic acids and an.olefin, including olefinic monomers and/or olefin poly-

30. mers. These acrylic acids, also referred to as "olefin acids" herein, exhibit olefin functionality and carboxylic acid functionality. Essentially any olefin acid

capable of incorporating carboxylic acid functionality onto a polyolefin backbone will provide copolymers suitable for use in blends of this invention. Preferred olefin acids include acrylic acid, H ₂ C = CH - COOH, and methacrylic acid, H,C = C(CH ₃ )COOH. Other acrylic acids which provide suit¬ able copolymers include straight chained aliphatic acrylic acids of from 3 to 20 carbon atoms, secondary and branch chained aliphatic acrylic acids of from 4 to 20 carbon atoms plus cycloalkyl acrylic acids of from 9 to 24 carbon atoms. Particular examples include crotonic acid, o-methyl acrylic acid, dimethyl acrylic acid, β-ethyl acrylic acid, atropic acid, propyl acyclic acid, etc. Halogenated and nitrosub- stituted derivatives of these olefin acids are also suitable copolymers, as are olefin acids with multiple carboxylic acid groups, such as itaconic acid.

Included within the scope of the functionalized polyolefins are those having carboxylic acid functional groups in their reactive ester form. The reactive esters are generally the lower alkyl (C, ₄ ) esters of the carboxy- lie acid functional groups. Examples of polyolefins suitable for use in this invention are the random, graft and block copolymers obtained by polymerization of olefinic monomers and/or olefin polymers with the lower alkyl esters of acrylic and methacrylic acid, such as methyl, ethyl and butylacrylate and methacrylate, preferably methylmethacry- late. Although the copolymers produced from these esters do not provide acid functionality, these ester groups are sufficiently reactive to interact with the neutralizing agents introduced into the blend. The anhydride functionalized polyolefins which are suitable for use in these blends are the graft, random and block copolymers obtained from reaction of maleic anhydride and olefin monomers and/or polyolefin polymers described

below. Copolymerization will provide a polyolefin having functional groups of the formula indicated below,

wherein R is hydrogen, alkyl of from 1 to 4 carbon atoms and alkenyl of from 2 to 4 carbon atoms. The open carbon bonds represent linkages to the carbon backbone. Incorpo¬ rating anhydride functionality onto a polyolefin backbone can be achieved by copolymerization processes well known to the art, such as those described in the Encyclopedia of Polymer Science and Technology, Volume I, 1964, pp. 76-84, which is incorporated herein by reference.

The preferred olefinic monomers which will react with the acrylic acids and esters to provide functionalized polyolefins include aliphatic hydrocarbons of from 2 to 15 carbon atoms plus alkyl cyclic compounds of from 8 to 24 carbon atoms having at least one alkyl radical with vinyl functionality. Examples of suitable olefinic monomers include ethylene, propylene, 1-butylene, 3-methyl-1-buty- lene, 4-methyl-l-pentylene, 1-pentylene, vinyl chloride, vinylidene chloride, vinyl acetate, and the like, including diene-rubbers such as isoprene, butadiene, ethylene propy¬ lene and the like.

These acrylic acids and esters can also be grafted onto rigid, high molecular weight olefin polymers, which typically have a degree of polymerization greater than 500. Suitable polyolefin polymer backbones include polyethylene, polypropylene, poly(l-butene) , poly(3-methyl-l-butene) , polyvinyl chloride, poly(l-pentene) and the like.

Commercially available acid functionalized polyolefin copolymers which are particularly suitable for use in the blends of this invention fall under the designation of

TM

"Surlyn^"", sold by Dupont. When grafting the acrylic acids and esters onto the polyolefin polymer backbone, techniques well known to the art may be utilized. For example, polymerization onto the backbone may be achieved by introducing an initiator, e.g., benzoyl peroxide, to a solution of acrylic acid or acrylic ester and the polyolefin polymer or olefinic mono¬ mer. On raising the temperature of the emulsion, polymer¬ ization is initiated to provide the grafted side chains.

In a typical bulk polymerization procedure, 100 parts of olefin monomer (rubber) is mixed with about 100 parts of acrylic acid or acrylic ester, 0.5 parts of benzoyl peroxide and 0.5 parts of dimethylaniline. The temperature is raised from about 25 to 85°C during which polymerization proceeds to about 50% completion. Then 0.2 parts of endcap- per is introduced and the polymerization is complete. Other methods for preparing these acrylic resin modified polyolefin copolymers are disclosed in the Encyclo¬ pedia of Polymer Science and Technology, Vol. 1, (1966), pp. 203-207, and the Encyclopedia of Chemical Technology, 3rd Ed., Vol. I, pp. 394-701, which are incorporated herein by reference.

The extent of functionalization of the polyolefin can vary widely by simply varying the ratio of olefin monomer and/or olefin polymer to functionalize the monomer, i.e., acrylic acid, acrylic ester and aleic anhydride. Up to 50% of the monomeric units on the functionalized polyole¬ fin may contain a functional group. Preferably, 2 to 25% and most preferably, 3 to 20%, of the monomers contain functional groups. The amount of functionalized polyolefin

added to the polyphenylene ether/polystyrene resin may vary within broad limits also. Preferred concentrations range from about 1 to 25% by weight of the resinous components. In a preferred family of compositions, the polyphenylene 5 ether comprises from about 1 to about 95% by weight total resin, the functionalized polyolefin copolymer comprises from about 5 to 25% by weight total resin with functional groups ^* upon.3 to 20% of the monomers and the styrene compo¬ nent-comprises 1% up to the remainder by weight of the total

10 resinous, components of said composition.

Especially preferred are compositions in which the polyphenylene ether is poly(2,6-dimethyl-l,4-phenylene) ether and comprises from about 2 to 95% by weight total resin, the functionalized polyolefin is a copolymer of

15 methacrylic acid (3 to 10%) and ethylene (50 to 97%) and comprises from about 1 to 15% by weight total resin and- the styrene resin component is a rubber modified polystyrene and comprises from 1 up to about 75% by weight of the total resinous components.

20 A neutralizing agent is added to these blends so as to neutralize the functional groups on the polyolefins during blending. This serves to compatibilize the polyole¬ fin with the polyphenylene ether/polystyrene resins. The neutralizing agents are metal salts of fatty acids or a

25. combination of the precursors to these metal salts. The precursors' comprise the fatty acid and the metal in oxide form. The metal salts are believed to form upon the addi¬ tion of these precursors to a melt blend of polymers. The metal salts and metal oxide contain metals selected from the

30 ^' group consisting of manganese, zinc, copper, chromium, nickel, iron, titanium, antimony, alkali metal salts and alkaline earth metals, which preferably comprise magnesium, lithium, sodium, calcium, barium, potassium and cesium.

Combinations of these metals are suitable. Essentially any oxide form of these metals will generate a salt complex with the fatty acids described below. Those metal salts which have a melting point below 300°C, are suitable for use in this invention. The metal salts and fatty acids are prefer¬ ably utilized in a proportion of less than 25% by weight of the total composition and most preferably 1 to 10% by weight. The preferred metal salts are those which contain zinc, barium, calcium, magnesium, titanium and antimony. Where the neutralizing agent comprises a metal oxide/fatty acid combination, quantities of metal oxide less than 15% by weight of the total composition are typically used. At higher concentrations, the metal oxides function as fillers. Preferably, the metal oxides comprise less than 10% by weight of the total composition and most preferably, • about 0.1 to 5% by weight. The preferred concentration of metal oxide is dependent on the concentration of fatty acids in the blend and the quantity of functional groups present on the olefin components. The preferred metal oxides include zinc oxide, antimony oxide, magnesium oxide, calcium oxide, barium oxide and titanium oxide. The most preferred metal oxide is zinc oxide.

These metal oxides and metal salts of fatty acids can be introduced to the composition by compounding or melt-blending within an extruder, either separately or in combination with other components of the blend, including the styrene resin, functionalized polyolefins and/or fatty acids.

The fatty acid which forms part of the neutraliz- ing agent must have at least ten aliphatic carbon atoms. Fatty acids of a shorter chain length provide salts with very high melting points, i.e. above 300°C, which may crystallize in the blend without neutralizing the functional

groups. Suitable fatty acid include those represented by the general formula R'-COOH. Substituent R' is generally a straight or branched chained aliphatic hydrocarbon radical of from 10 to about 100 carbon atoms. These substituents 5 may have unsaturated carbon atoms within the chain, such as oleic acid and they may also be substituted with aromatic groups of from 6 to 20 carbon atoms, halogen and/or nitro groups. The common fatty acids, such as, stearic, oleic, linoleic and palmitic acids, are suitable for use in the

1Q ^" neutralizing agents as part of the metal salts or as a separate component in combination with the metal oxides. Suitable metal salts include calcium stearate, zinc, laurate, zinc stearate, magnesium laurate and aluminum ricinoleate. Although the quantity of fatty acid utilized

15 with- metal oxide can vary widely, quantities within the range of about 0.5 to 5% by weight of the total composition are. preferred. The fatty acid is preferably used in propor¬ tions which correspond to the concentration of metal oxide. Preferred ratios of metal oxide to fatty acid fall in the

20. range of about 5:1-4 with ratios of about 3:2 being most preferred. Excess quantities of fatty acid function as plasticizers and result in a heat distortion loss for the blend. These fatty acids can be introduced to the blend either alone or in combination with other components by

25 conventional blending processes.

By introducing the metal oxide and fatty acid to the melt-blend it is believed metal salts are generated which, in turn, neutralize the functional groups on the polyolefins. The enhanced compatibilization of the resinous

30 components eliminates delamination during processing. Although the mechanism is unknown, the improvement in properties is suspected to result from either plasticization

of the blend or the formation of an interpenetrating polymer network upon neutralization of the functional groups.

The metal salts and combinations of metal oxide and fatty acid compatibilize so efficiently that the use of a matrix compatibilizer with aromatic moieties is unneces¬ sary. The term "matrix compatibilizer" as used herein refers to polymers with constituents similar to those within the functionalized polymer and those within the polypheny¬ lene ether/polystyrene blend. These matrix compatibilizers exhibit some degree of compatibility with each of the blend components and serve as intermediates between the incompati¬ ble constituents.

Matrix compatibilizers for the blends of this invention typically exhibit acid, ester, or anhydride functionality in combination with an aromatic moiety such as styrene or polyphenylene ether polymer backbone. Examples include sulfonated polystyrene and styrene-acrylic acid copolymers. These matrix compatibilizers may be introduced into the blends of this invention if desired. However, an object of this invention is to avoid their use so as to provide blends with higher impact strength and improved environmental stress crack resistance.

Additives other than the matrix compatibilizer may be present in the compositions of this invention such as plasticizers, pigments, impact modifiers, flame retardants, fillers, stabilizers, anti-static agents, mold release agents, etc. in amounts ranging up to about 30%, preferably 15% by weight of the total composition. Chemical compounds useful for these purposes and the quantities necessary to provide the desired additive effect will be apparent to those skilled in the art. It is particularly desirable to introduce phosphorous compounds such as triphenyl phosphate which provide both plasticization and flame-retardance to

these compositions. These additives are available commer¬ cially from FMC Chemical under the trade name Kronitex-50.

Particularly useful embodiments of this invention are those blends which are impact-modified with butadiene rubbers, isoprene rubbers and the like. These blends not only show improved impact strength, as tested by Izod impact values, they also maintain the resistance to stress cracking provided by the metal oxide/fatty acid neutralizing agent combination. The extent of impact strength enhancement ? depends on the impact modifier introduced. Impact strength has been found to increase with the molecular weight of the rubbers. Suitable impact modifiers are the Kraton series manufactured by Shell Oil Co. These impact modifiers are preferably introduced in proportions ranging from about 1 to 5 15% by weight.

The method of forming the polymer composition is not critical, with prior art blending techniques being suitable. For example, extruding the blend and chopping it into pellets suitable for molding may be achieved by means ' conventionally used to prepare similar solid thermoplastic compositions. In another method, the acrylic acid or ester polyolefin copolymer is blended with water to form an aqueous dispersion which is added directly to a solution of the polyphenylene ether such as toluene. The resins are ? precipitated, e.g., by adding methanol, and the precipitate is further mixed by extrusion or coextrusion with styrene resin.

All of the U.S. patents cited above are incorpo¬ rated herein by reference. The following examples are provided to illustrate particular embodiments of this invention. It is not intend¬ ed to limit the scope of this invention to the embodiments described within these examples.

EXAMPLES 1-4

The polyphenylene ether (PPO ) was obtained from General Electric Company and exhibited an intrinsic viscosi¬ ty of from .49 to .53. The polystyrene resin utilized was high impact polystyrene (HIPS) produced and designated polystyrene 851 by Foster Grant. The acid functionalized polyolefin, Surlyn TM, was an ethylene-methacrylic acid

(3-9%) copolymer used as received from Dupont and was of

Grade 1555. Where utilized, the styrene-acrylic acid copolymer contained 5% acrylic acid. These styrene-acrylic acid copolymers were obtained from General Electric Company. The components of the blends described below were tumble mixed in a jar mill for about 1 hour. This dry blend was then compounded using a Welding Engineer 0.8" extruder operating at a screw speed of 300 to 400 rpm, a feed rate of 5 to 10 pounds per hour and a temperature profile as indica¬ ted below.

Zone 1=250°F, Zone 2=350°F, Zone 3=450°F, Zone 4=500°F,

Zone 5=500°F, Zone 6=550°F, Die=550°F.

The extrudate was pelletized, dried and injection molded on an Engel model 28 molding machine. The melt temperature was maintained at about 530°F while the mold temperature was maintained at about 100°F, (conditions known to promote stress cracks. ASTM mold parts were obtained which included Izod, tensile, and heat distortion tempera¬ ture bars and a Gardner plaque. These parts were heat aged at about 190 to 200°F so as to accelerate the formation of stress cracks. The parts were inspected for stress cracks on their edges since this phenomena correlates with the

degree of solvent resistance. Parts which showed small edge cracks only on the heat distortion temperature bars upon visual inspection were considered to exhibit "slight" levels of stress crack formation while those which exhibited edge cracks on the heat distortion temperature bar, tensile and Izod bars were considered to exhibit "significant" levels of stress crack formation. Delamination was also measured by visual inspection of fracture surfaces on the Izod bars. Four blends (1-4) were produced having composi- tions as indicated in Table I. The stress crack evaluation, delamination and Izod impact properties for each blend are given in Table II.

Table I

Stearic

Example PPO ^R HIPS Surlyn™ K-50* ZnO Acid SAA**

1 50 40 - 13 - - -

2 50 40 7 13 - - -

3 50 40 7 13 3 2 9

4 50 40 7 13 3 2 _

* K-50 = Kronitex-50 triaryl phosphate plasticizer ** SAA = styrene-acrylic acid copolymer

Table II

Property Profiles fo:r Blends 1- ^■ 4

Izod ft./lb.

Example Extent of Crack Delamination* Inch of notch

1 Significant None 3.5

2 Slight Severe 1.6

3 Significant None 1.7

4 None None 1.7

* as determined visually on an ASTM part

The data demonstrates that PPO/HIPS/Surlyn blends with contain ZnO and the fatty acid, stearic acid (4) show improved resistance to delamination without a compatibili¬ zer. In addition, where the compatibilizer is absent, an improvement in the resistance to stress cracking is obtain¬ ed.

EXAMPLES 5- 11

In Examples 5-10, the polyphenylene ether, HIPS, Kronltex-50 and Surlyn-1555 were as utilized in Examples 1-4-. An impact modifier of the Kraton series was addition- ally added to the blends of these examples, which comprised PP.O, HIPS, Surlyn, Kraton G, and Kronitex-50 in the follow¬ ing weight proportion 50/40/9/5/13. These blends were compounded and molded as indicated in Examples 1-4. The quantity of zinc oxide and stearic acid plus the impact properties and delamination characteristics of these blends are indicated within Table III.

Table III

Property Profiles for the Blends of Examples 5' -10

Gardner Tensile

Stearic Kraton Impact Elong.

Ex. ZnO Acid (Grade Izod (in./lb.) (%) Delam.

5 ^" _ - - - 2.0 125(brittle) 22 Severe

6-- - - 5(1651) 3.0 125(brittle) Severe

7 5 2 5(1651) 4.3 450(ductile) 159 None

8 - 2 5(1651) - _ Severe

9 5 - 5(1651) - - Slight

10 5 2 5(1650) 10.8 141 None

11 5 2 5(1652) 11.1 127 None

The results of Table III show that severe delamin- ation results where the acid modified polyolefin is intro¬ duced into the blend either alone or in combination with an impact modifier. In addition, poor impact and tensile

properties are obtained. However, where a neutralizing agent, zinc oxide and stearic acid are introduced to such blends, a substantial improvement in impact properties is obtained and no delamination results. The results of entries 8 and 9 demonstrate that the use of stearic acid or ZnO alone does not suppress the delamination. Examples 10 and 11 illustrate the effects of utilizing different grades of impact modifiers.

EXAMPLES 12-14

In Examples 12-14 a comparison is made of the stress crack resistance of three blends with varying amounts of acrylic resin modified polyolefin. The polyphenylene ether, HIPS, Kronitex-50, Surlyn, Kraton G (1651) were as used in Examples 1-4 and 5-11. Each of the three blends contained 50 parts PPO , 40 parts HIPS and 13 parts Kroni- tex-50. The remaining components are shown in Table IV with the numbers representing parts by weight. These blends were compounded and molded as indicated in Examples 1-4. The extent of stress cracking which appeared on the molded parts is also provided in Table IV.

Table IV

Stress Cracking for Blends of Examples 12 .-14*

Stearic Crack

Example Surlyn ZnO Acid KG-1651 τio ₂ length (cm)

12 9 3 2 5 5 0

13 7 3 2 5 5 5

14 * _" 10-15**

* parts by weight ^* typical value

Examples 12-14 illustrate the addition of a carboxylic acid functionalized polyolefin reduces the extent of stress crack formation, which is indicative of improved solvent resistance.