THERMOPLASTIC COMPOSITION HAVING IMPROVED IMPACT MODIFIER AND PROCESS FOR PRODUCTION

Abstract: Thermoplastic composition having an improved impact modifier. In an admixture of polyphenylene ether and butadiene-modified alkenyl aromatic resin, a resin which is a network polymer combining poly-alkenyl aromatic and polybutadiene membrane is employed. On subjection to high shear, the continuous membrane phase is shredded into discrete segments which impart an increased impact strength to the composition.

Description: -ι- Descriptioή Thermoplastic Composition Having Improved Impact * Modifier and Process for Production Background of the Invention - Polyphenylene ethers ara Jaown ωd described in numerous publications including C.S. Patent Nos. 3,306,374 and 3,306,375 of Allan S. Bay and U.S . Patent Nos. 3,257,357 and 3,257,353 of Geiu Staaatofifi. The high molecular weight pσlyαers are high performance engineering thermoplastics possessing relatively high selt viscosities and softening points (i.e., in excess of 275*C.) and are useful for many commercial applications requiring high temperature resis¬ tance including formation of fills. fiber and molded articles. While their high performance properties are most desirable, the relatively high melt viscosities and softening points of these polyphenylene ethers are often a disadvantage. For example, although they may be employed to produce superior molded articles by melt processing techniques, the. high tasipera- ' uras required are undesirable. 3ecause of low cost and an overall combination of fair to good properties, aikenyl aromatic resins such as poly¬ styrene have found wide and diversified commercial acceptance. However, such resins are usually brittle, possess relatively low heat distortion temperatures and have relatively poor resistance to the more common organic solvents. Therr.opiasi._ic compositions cαn-_____i___ing polyphenylene ether (or αxiάe) in admixture with aikanyl aromatic resins resolve many of the drawbacks of these two individual resins. Examples are, for instance, described in U.S. Patent No. 3,333,435 of Ξric P . Cice , the disclosure of which is incorpor¬ ated herein by reference. Such compositions ars r_=st generally employed in the production of molded and/or extruded articles. It is known in the art that various of these properties of these compositions may be further izproved by cαpolymerizing the alkenyl aromatics with other monomers or by blend-Lag with other resins. Modifiers such as butadiene, for example, are customarily incorporated into the alkenyl aromatic resins to im¬ prove the properties of the resultant compositions. Such modi¬ fied resins provide means for overcoming various physical draw¬ backs of alkenyl aroπatic resins, particularly polystyrene, while simultaneously facilitating the processing of polyphenylene ethers. . __. - As is described inςhe art, butadiene modification of alkenyl aromatic resins may take many forms. Poiybutadiene or oopoiymers partially derived from butadiene may be graft, block or otherwise polymerised with such alkenyl aroπatic resins. The resultant product may also be unsaturated or satura-εed (for example, by subsequent hydrogenation} without loss αf desirability. Despite the varied and diverse means for preparing these modified resins, the prior art approaches have generally involved polymerization techniques which developed a continuous alkenyl aromatic phase containing a discrete and discontinuous bu-sadiene phase. These approacnes are known to result in im¬ proved polyphenylene ether compositions. An al smative b _adiene aodifiad-poiyaikeny arc__:a---.c form of resin —i.e. , one in which there is a continuous phase including butadiene — is known. Their preparation is described in Polymer Engineering and Science, Vol. 17, page 498. Such resins have not, however, been employe--, with polyphenylene ethers. No substantial uses have been found for them and they have therefore been largely ignored. It has now been discovered that this latter class of modified resins may be utilized in producing improved poly¬ phenylene ether compositions. Such compositions, incorporating butadiene-modified alkenyl aromatic derived from a resin having a continuous phase which is butadiene-based, exhibit highly desirable impact strengths and other physical and processing properties. Introduction to the Invention - The present invention relates to improved thermoplastic compositions comprising an admixture of polyphenylene ether and butadiene-modified alkenyl aromatic resin. For these compositions, the butadiene-modified resin is a network polymer combining pol lkenyl aromatic and polybutadiene membrane. On being subjected to high shear, the continuous membrane phase is shredded into discrete segments which impart an increased impact strength to the composition. Description of the Invention - The polyphenylene oxida and modified resin useful in accordance with the present kinds of compositions are, as previously indicated, individually well known and readily available. There are, however, various preferred composition components. These are primarily ones corsncniy having applications for which high impact strength is particularly desirable. ,__ The preferred polyphenylene ethers are of the formula: wherein Q is selected from the group consisting of hydrogen, hydrocarbon radicals, halohydrocarbon radicals having at least two carbon atoms between the halogen atom and the phenβl nucleus, hyάrocarbonoxy radicals and halohydrocarbonoxy radicals having at least two carbon atoms between the halogen atoms and the phenol nucleus, Q' and Q* are the same as Q and in addition, halogen with the proviso that Q and Q' are preferably free of a tertiary carbon atom; and n is an integer of at least 50. t Especially preferred is poly(2,S-d___me l-l,4- _ phenylene) ether. The alkenyl aromatic resins are likewise well known and are preferably derived from monomers of the formula: - -< wherein and R are selected from -i>~ group consisting of lowei alkyl or alkenyl groups of from 1 to 5 carbons. s and R are SA*lt→.t-ά f om the group consisting of chloro, bromσ, hydrogen and lower alkyl of from 1 to 6 carbon atoms. R° and are selected from the group consisting of hydrogen, halogen and lower alkyl and alkenyl groups o .from 1 to S carbon atoms or 3 K. - aanndd RR 6 mmaayy bbee σcoonnccaatteeπn.ated together with hydrocarbyl groups ___o form a naphthyl group. Specific examples of alkenyl aromatic monomers include s yrene, chlorσstyrene, alpha-methylstyrene, vinyl xylene, άi inyl-benzene and vinyl naphthalene. These components of the present compositions may be admixed in any proportion. Widely divergent proportions ara known for such types of composition. More desirable, they are in a weight ratio of from about 1:5 to 5:1, most preferably about 1:1 for use in the present compositions. The modified resins utilized in accordance with the present invention are network polymers combining polvalkenyl aroπatic and polybutadi-sne membrane. These network polymers are characterized in that, upon initial formation, they exhibit a continuous phase of polybutadiene membrane. This membrane enve¬ lops a phase of polyalkenyl aromatic which may either be in dis¬ continuous or continuous form. The key portion of these network polymers, the _-___-ara_5e, w&γ consist essentially of pciymeri-ied bm_aύe__e (by n cπ tara it is meant to include alkyl derivatives of bu-cadiene s such as isoprene) . In addition, however, other monomers may be incorporated in addition to the butadiene. Host commonly, for example, snoήσ-ole in such as styrene is included to form poly¬ butadiene interpoly er. In the pαlyalkenyl aromatic resins of the present invention, about 3 to 15* and preferably about 5% to 10% of modi¬ fier by total weight is employed. This amount of, for example, polybutadiene provides optimization of composition properties. These network polymers may be produced by a variety of known techniques. 3utadiene can, for example, be polymerized without stirring in a solution of polyalkenyl aromatic. Alternatively, stirring of such reagents may be interrupted prior to phase inversion and polymerization completed under low shear. Another class of network polymers can be made by swelling cross-linked polybutadiene with alkenyl aromatic monomer and then polymerizing the monomer. Polymers of this type are known as semi-interpenetrating network polymers. The polyphenylene ether and modified resin may be mixed in any manner. For ultimate application, the admixture should be essentially homogeneous. Even a heterogeneous σσm- nosi ion may be prepared initially since it has been _5_r__nd ba con¬ ventional molding and/or extrusion to final form will provide sufficient high shear to break down the membranous ra-^rix (or cellular structure) and produce an essentially homogeneous comoosition. 7 In the resultant homogeneous composition, the polyphenylene ether and polyalkenyl aromatic resin become the only continuous phase. However, the formerly continuous phase of polybutadiene membrane is residually evidenced by discrete segments of the membrane dispersed essentially unifomly within the composition. These segments of the matrix membrane commonly consist of small, isolated sheets or the like, dependant on the physical configuration that the membrane originally exhibited when continuous and intact. They are ordinarily less than about 5, most desirably from about 1 to 2, icrons across; --less than about 500, most desirably from about 100 to 300., Angstroms in thickness. Ξven in segment form, the polybutadiene membrane re¬ tains the rubbery characteristics of the initial network polymer - Once prepared, the present composition may be utiliz¬ ed for any of the diverse purposes for which similar polypheny¬ lene oxide/polyalkenyl aromatic resin compositions have already been employed. They are most commonly used in molding powder formulations, either alone or mixed with other polymers such as the polyolefin. They may also contain various conventional fill¬ ers to make molded parts. They are ordinarily used to prepare oi ed (by injection or compression) or extruded articles. These articles may possess a broad spectrum of forms including sheets, rods, etc. The present composition may also contain such additional ingredients as yes, pigmen s, stabilizers, piasti- cizers,. fire retardanns ate. All t ese may be incorporated in conventional manner for the purooses for which thev ara known. " U _:. A→ . o The following examples are given by way of illus¬ tration only and are not. intended as a limitation on the scope of this invention. Many variations are possible without departing from its spirit and scope. Unless otherwise specified herein, all proportions are provided on a weight basis. ΞXAWPL2 I A solution of SO g of X53O-C-502 rubber, a low molecular weight, high cis polybutadiene rubber made by 2olysar> itd. , in 940 g of styrene is transferred to a 4 liter stainless steel reaction vessel with 1.2 g of tert-hutyl peracetate and stirred, under nitrogen, for three hours at 100 β C. -The mixture is suspended in 1500 ml of hot water containing, 4 g of poly (vinyl alcohol) and 3 g of gelatin. 3 g of di-tert-butyl peroxide is added and the polymerization is completed by heating for one hour at 100 a C, two hours at 12ø β , 1 hour at 140" and finally for two and one-half hours at 155'C. The mixture is cooled and the product, in the form of fine beads, is filtered off, washed with water, and dried. One ram of the polymer beads is stirr.ed overnight with 25 ml of toluene. The polymer beads swell, but cc not disintegrate, a characteristic of rubber polystyrene systems in which the continuous phase is made up of cross-linked rubber. A portion of the beads is compression molded into a 1/3" sheet ana examined in thin section by transmission electron necro¬ scopy after staining with osmium tetroxidei It has a cellular, structure with the continuous rubber or polybutadiene phase forming a continuous network. 9 2Xa_MPI5 II A mixture of 50 parts of polyphenylene ether, 50 parts of the polymer prepared in Example I, 3 parts of triphenyl phosphate, 1 part of tridecyl phosphite, i.S parts of polyethy¬ lene, 0.15 parts of zinc sulfide and 0.15 parts of zinc oxide is extruded in a twin-screw extruded and then molded into 1/3" Izod test bars in a screw injection molding machine. One gra - of the molded plastic is cut into small pieces and stirred over¬ night in 25 ml of toluene. The suspension is transferred co a tared centrifuge tube and centrifuged for 70 minutes at about 12,000 rpm. The liquid phase is decanted and z e residua re- suspended in 50 ml of toluene for one day, then again centri¬ fuged and the toluene solution decanted. The weight of swollen gel is determined and the gel is dried under vacuum. The weight of toluene-insoluble gel, after correction for the small amount of insoluble zinc ccrpounc, is 7.0% of the sample, with a swelling index of 13.1. The swelling index is typical of that of the rubbery phase in ordin¬ ary high impact polystyrene, while the amount of gel (7.0%, com¬ pared to 2.9% calculated from the weight of rubber present) in¬ dicates than the rubber is grafted with polystyrene to about the same extant as in ordinary high impact polystyrene. The product, differs from that made from ordinary high impact polystyrene in the morphology of the rubber phase. Transmission electron micro¬ scopy of the molded material shows that the rubber membranes of the polystyrene were broken into individual, well dispersed thin* sheets, about one to two rsicrons long and only a few hundred Angstroms _-. hicxness. 10 The notched Izod impact strength of the 50:50 composition is shown below in the Table, along with that αf two 50:50 compositions made with polystyrenes containing other modifier rubbers as the dispersed phase. The poly¬ styrenes were extruded, when necessary, with 3ylene 8G polystyrene homopolymer to make the rubber content six oercent in each case. _.A3ZS Izod Impact Modified for Alkenyl Aromatic Sas n ■lbs/inch of notch) 3xa___.ple X 3-7 Foster-Grant 334 2.4 3lendex 625 1.9 These comparative results shew the unexpectiy high increase in impact strength conferred upon the present com¬ positions by the present network polymer over conventionally modified polyalkenyl aromatic resins. A solution 130 g of Solprene 303, a block copolyme: of butadiene and styrene, in 1520 g of styrene s placed in a stainless steel reactor with 2.15 g αf dicumyi peroxide and i.d of tert-dodecyl aerca tan. The reactor is purged with nitrogen, pressurized to 15 psig with nitrogen, and stirred for four hours at 115 β C. The mixture is suspended in 1500 ml of water containing 3.5 g αf gelatin and 4.5 g of ?cly .vmyi. alcohol) and polymerization is completed by heating - H. 11 the suspension for fire hours at 120*C and then for five hours at 140 β C. The resultant polymer beads ara filtered off, washed with water, dried, and extruded in a single screw extruder. The extruded pellets are opaque. Examination by a transmission electron micrograph shows a network structure, with a continuous rubber phase. A mixture of 30 parts of polyphenylene ether, 20 parts of extruded pellets described above, and 5 parts αf triphenyl phosphate is extruded in the single-screw axtruder and the extruded pellets then molded into standard test pieces with a screw injection molding machine. , The product is almost transparent and moderately tough. A second examin¬ ation by transmission electron micrograph shows that, during high shear extrusion with polyphenylene ether, the rubber network of the SIPS broke down. The product now contains rubber present as discrate small particles, mostly of the "capsule" or core shell type. Testing provides the following date: Elongation 523 Tensiit ' yield Surength 11 , 400 psi Irod ϊnpact strength 2.9 ft . lbs ./inch of notch Gardner Xmpact Strength 175 in. lbs . Heat Distortion Ta erature 233 β ? Average 3urn Tiam, UX.-94 4 .3 sec . All of the above sen iαned patents and/or publications are incorporated herein by reference. 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 nay be aade in the particular eα_bodi____ents of the invention described which are within the full intended scope of the invention as defined by the appended claias.

Claims: 13 Claims 1. In a thermoplastic composition comprising an admixture of polyphenylene ether and butadiene-modified alkenyl aromatic resin, the improvement wherein said resin comprises network polymer combining polyalkenyl aromatic resin and polybutadiene membrane. 2. The composition αf Claim 1, wherein the poly¬ butadiene πenbrane forms a continuous phase in said resin. 3. The composition of Claim 2, wherein the poly¬ phenylene ether and resin are in a weight ratio αf from about - to 5:1. 4. The composition of Claim 2, wherein the resin comprises from about 3 to 12% membrane by total composition weight. 5. The composition of Claim 2, wherein the alkenyl aromatic resin comprises polystyrene. 6. The composition of Claim 1, wherein the resin comprises discrete polybutadiene membrane segments dispersed within said composition. 7. The composition of Claim S, wherein the poly¬ phenylene ether forms a continuous phase in ' said composition. 1 3. The composition αf Claim 6 wherein the poly¬ phenylene ether and resin are is a weight ratio of from about 1:5 to Ssl. 9. The composition αf Claim 6 wherein the resin comprises from about 3 to 15% membrane segments by total com¬ position weight. 10. The composition of Claim 6 wherein the poly¬ alkenyl aromatic resin comprises polystyrene. 11. A process far producing the composition of Claim S comprising subjecting an admixture of polyphenylene ether and network polymer combining polyalkenyl arα_fiatic resin and a continuous phase of polybutadiene membrane to high shear sufficient to produce-discrete polybutadiene membrane segments 12. The process of Claim 11, wherein the cαs-sositiαn is molded. fυR£

Inventors: COOPER GLENN D
Applicants: GEN ELECTRIC, GENERAL ELECTRIC CO
Application year: 1981
Main classification: C08L9
IPC codes: C08L51, C08L71