HIGH IMPACT POLYPHENYLENE ETHER COMPOSITIONS

Abstract: Thermoplastic poly(phenylene ether) (PPE) compositions having improved impact strength and reduced modulus loss are disclosed. These compositions are based on a mixture of PPE and an elastomeric interpolymer of a C1 to C4 isomonoolefin, e.g. isobutylene, and a para-alkylstyrene comonomer, e.g. para-methylstyrene. The interpolymer may also contain benzyliques functional groups such as halogen.

Description: HIGH IMPACT POLYPHENYLENE ETHER COMPOSITIONS BACKGROUND OF THE INVENTION The invention relates to toughened polymer compositions based on a poly(phenylene ether) blended with an isomonoolefin/para- aL ylstyrene copolymer. Poly(phenylene ether) (PPE) resins are well known engineering thermoplastics possessing relatively high melt viscosities and softening points, e.g. in excess of about 275 β C. These polymers are useful in many applications where good mechanical properties and heat resis- tance are required. On the negative side, the PPE's generally suffer from poor impact resistance and poor processability. For example, the room temperature notched Izod impact strength of PPE's is generally below 1 ft.-lb. in. The intrinsic viscosity of a typical PPE is about 0.50, which is not suitable for processing by the usual injection molding technique. U.S. Patent 3383435 teaches that the processing characteristics of PPE resins may be improved by forming blends of PPE and com¬ patible styrene polymers, e.g. polystyrene or copolymers of styrene with acrylonitrile. Impact properties are also improved by using high impact polystyrene as a blend component. High impact polystyrene is a product which may be prepared by solution polymerization of styrene in the presence of a dissolved elastomer, e.g. cis-polybutadiene, such that the final product consists of a polystyrene matrix having from about 1-20% by weight of a discreet phase of polybutadiene particles dispersed therein. Other polymer additives used to improve the impact and proc¬ essing properties of PPE include hydrogenated sty- rene/butadiene/styrene block copolymers as disclosed for example by J.P. Kirkpatrick et al., Εlastomerics", October 30, 1988, p. 30-32. A disadvantage of using a polybutadiene-containing impact modifier is that the polybutadiene segment tends to partially degrade at the high temperature required to process PPE, e.g. 290 °C or greater. The use of hydrogenated styrene/butadiene/styrene block co- polymers as an impact modifier generally gives rise to a composition having substantially reduced modulus which is undesirable in many applications. SUMMARY OF THE INVENTION The present invention provides for thermoplastic polymer com- positions having improved impact strength and reduced modulus loss comprising a blend of: a) a poly(phenylene ether) polymer; and b) an interpolymer of a C 4 to C 7 isomonoolefin containing from about 0.5 to 20 mole% of copolymerized para- alkylstyrene. Preferred blends contain from about 1 to about 100 parts by weight of the isomonoolefin interpolymer per 100 parts by weight of the PPE. The isomonoolefin interpolymer also includes functionalized interpolymers prepared by replacing a portion of benzylic hydrogen with functional groups such as halogen or other functional groups such as acrylics. The composition may also contain one or more additional modifier polymers such as an olefin polymer, and/or styrene-based polymer. The compositions may be melt blended and molded or extruded to form molded articles exhibiting improved impact, modulus and stiff- ness properties. DETAILED DESCRIPTION OF THE INVENTION The C < -C 7 isoolefin/para-alkylstyrene interpolymers used in the invention are random copolymers of a C 4 to C 7 isomonoolefin, such as isobutylene and a para-alkylstyrene comonomer, preferably para- methylstyrene containing at least about 80%, more preferably at least about 90% by weight of the para-isomer, and also include functional- ized interpolymers wherein at least some of the alkyl substituent groups present in the styrene monomer units contain halogen or some other functional group. Preferred materials may be characterized as isobutylene interpolymers containing the following monomer units randomly spaced along the polymer chain: 1. and optionally 2. 2 . wherein R and R 1 are independently hydrogen, lower alkyl, preferably C, to C 7 alkyl and X is a functional group such as halogen. Preferably R and R 1 are each hydrogen. Up to about 60 mole % of the para- alkylstyrene present in the interpolymer structure may be the func- tionalized structure (2) above. Where monomer units 2 in the above formula are absent, then the isomonoolefin interpolymer is non-functionalized, i.e., is a random copolymer of isomonoolefin and para-alkylstyrene. The most preferred of such interpolymers are copolymers of isobutylene and para- methylstyrene containing from about 0.5 up to about 20 mole % of para-methylstyrene randomly copolymerized along the polymer chain. Where monomer units 2 in the above formula are present, the isomonoolefin interpolymer is at least a terpolymer containing from about 0.5 up to 60 mole % of functionalized monomer units 2 based on the content of aromatic monomer units 1 and 2. The functional group X may be halogen or some other functional group incorporated by nu- cleophilic substitution of benzylic halogen with other groups such as alkoxide, phen oxide, carboxylate, thiolate, thioether, thiocarbamate, dithiocarbamate, thiourea, xanthate, cyanide, malonate, amine, amide, carbazole, phthalamide, maleimide, cyanate and mixtures thereof. These functionalized isomonoolefin interpolymers and their method of preparation are more particularly disclosed in U.S. Patent 5,162,445, the complete disclosure of which is incorporated herein by reference. Most useful of such functionalized materials are elastomeric random interpolymers of isobutylene and para-methylstyrene contain¬ ing from about 0.5 to about 20 mole % para-methylstyrene wherein up to about 60 mole % of the methyl substituent groups present on the benzyl ring contain a bromine or chlorine atom, preferably a bromine atom. These polymers have a substantially homogeneous composi¬ tional distribution such that at least 95% by weight of the polymer has a para-alkylstyrene content within 10% of the average para- alkylstyrene content of the polymer. More preferred polymers are also characterized by a narrow molecular weight distribution (Mw Mn) of less than about 5, more preferably less than about 2.5, a preferred vis¬ cosity average molecular weight in the range of from about 200,000 up to about 2,000,000, and a preferred number average molecular weight in the range of from about 25,000 to about 750,000, as determined by Gel Permeation Chromotography. The interpolymers may be prepared by slurry polymerization of the monomer mixture using a Lewis Acid catalyst, followed by halo- genation, preferably bromination, in solution in the presence of halo- gen and a radical initiator such as heat and/or light and/or a chemical initiator. Preferred interpolymers are brominated interpolymers which generally contain from about 0.1 to about 5 mole % of bromomethyl groups, most of which is monobromomethyl, with less than 0.05 mole % dibromomethyl substituents present in the copolymer. More preferred interpolymers contain from about 0.05 up to about 2.5 wt % of bromine based on the weight of the interpolymer, most preferably from about 0.05 to 0.75 wt % bromine, and are substantially free of ring halogen or halogen in the polymer backbone chain. These interpolymers, their method of preparation, their method of cure and graft or functionalized polymers derived therefrom are more particularly disclosed in the above referenced U.S. Patent No. 5,162,445. Poly(phenylene ether) (PPE) thermoplastic engineering resins which are modified in accordance with this invention are well known, commercially available materials produced by the oxidative coupling polymerization of alkyl substituted phenols. They are generally linear, amorphous polymers having a glass transition temperature in the range of about 190 °C to 235 °C. Preferred PPE materials comprise the structure: wherein Q is a monovalent substituent group selected from halogen, hydrocarbon having less than 8 carbon atoms, hydrocarbonoxy and halohydrocarbonoxy. More preferably, Q is the same or different alkyl group having from 1 to 4 carbon atoms and n is a whole integer of at least 100, preferably from 150 to about 1200. Examples of preferred polymers are poly(2,6-dialkyl-l,4-phenylene ether) such as poly(2, 6- dimethyl-1, 4-phenylene ether), poly(2-methyl-6-ethyl-l, 4-phenylene ether), poly(2-methyl-6-propyl-l, 4-phenylene ether), poly-(2, 6- dipropyl-1, 4-phenylene ether) and poly (2-ethyl-6-propyl-l, 4- phenylene ether). In order to achieve enhanced impact resistance and processing properties, the PPE and isomonoolefin interpolymer (I-PMS) are melt blended at a ratio in the range of from about 1 to about 100 parts by weight of I-PMS per 100 parts by weight of the PPE, more preferably from about 5 to about 50 parts by weight of I-PMS, and most preferably from about 15-50 parts by weight I-PMS per 100 parts by weight PPE. As stated above, blends containing PPE and the isomonoolefin interpolymer additive exhibit improved physical properties as com¬ pared with PPE without the added interpolymer. These properties are found to be even more enhanced where the interpolymer contains a benzylic functional group such as halogen, e.g., bromine which is ca¬ pable of interacting with PPE under mixing conditions. It is believed that these enhanced properties are achieved as a result of a chemical interaction between benzylic halogen, e.g. bromine, present in the halogenated interpolymer and displacable hydrogen present in the PPE, probably an electrophilic substitution reaction, which occurs when the polymers are melt blended at temperature in the range of about 280 to about 310 °C. This reaction may be further promoted by inclusion of a catalyst in the formulation which will promote the elec¬ trophilic substitution reaction, such as zinc oxide, magnesium oxide, zinc bromide, ferric chloride and the like. These promoters may be added at a level in the range of from about 0.01 to about 1.5 wt. %, more preferably from about 0.05 to about 0.5 wt. %, based on the con¬ tent of halogenated interpolymer present in the composition. The I-PMS interpolymer has a saturated backbone structure which makes it very stable during melt blending, unlike prior art im¬ pact modifiers which contain unsaturated diolefin polymers, e.g. poly¬ butadiene. Consequently, the blend components may be compounded using any suitable melt mixing device such as a Banbury Mixer, or, most preferably, in a mixer/extruder. Preferred melt mixing tempera¬ tures are in the range of from about 270° to about 320 °C, more pref¬ erably from about 280° to about 310 °C, for a period of mixing time sufficient to achieve a uniform dispersion of the I-PMS interpolymer within the PPE matrix, generally about 0.5 to about 4 minutes. The melt processability of the composition may be further con¬ trolled by including a vinyl aromatic polymer or copolymer in the com¬ position. Examples of such polymers are polystyrene and copolymers of styrene with less than 50 wt. % of acrylonitrile. A good balance be¬ tween impact strength and processability can be achieved by varying the contents of vinyl aromatic polymer in the PPE/I-PMS blends. The level of addition of vinyl aromatic polymer may also range from about 1 to about 100 parts by weight per 100 parts by weight of PPE, more preferably from about 5 to about 60 parts by weight per 100 parts by weight PPE. Since the I-PMS interpolymer is quite tacky even at room tem¬ perature, it may be desirable to first form a masterbatch composition of the I-PMS mixed with another polymer such as an olefin polymer, melt blend and extrude the mixture to form non-tacky pellets. Pelletizing facilitates the compounding. These pellets may then be melt blended with the PPE to form the compositions of this invention. Suitable ole¬ fin polymers include one or a mixture of crystallizable polymers such as polypropylene, high density polyethylene and ethylene/propylene copolymers as well as amorphous polymers such as low density poly¬ ethylene and copolymers of ethylene/propylene and up to 10 wt. % of a non-conjugated diene such as norbornadiene, 1, 4-hexadiene, dicy- clopentadiene, and the like. Generally speaking, these masterbatch pre-blends may contain from about 20 to 95 wt. % of the I-PMS co- polymer and the balance one or a mixture of the olefin polymers. Tack may also be reduced by pre-dusting the I-PMS copolymer, e.g., a bro- minated I-PMS copolymer, with zinc oxide or other of the powdered re¬ action promoters described above. The compositions of this invention may also include effective amounts of other ingredients normally included in PPE compositions including antioxidants, pigments, colorants, fillers, plasticizers and the like. The following examples are illustrative of the invention. The material identified in the following description as Exxpro ™ elastomer is a brominated interpolymer of isobutylene and para-methylstyrene (PMS) containing 4.7 wt. % PMS, 0.15 mol % of benzylically bromi¬ nated PMS (measured by NMR), 0.35 wt. % bromine based on the weight of the polymer (measured by X-ray fluorescence) and the inter¬ polymer has a viscosity average molecular weight of 350,000, measured as a dilute solution in diisobutylene at 20 °C. The material identified as XP-50 is a non-functionalized copolymer of isobutylene containing 5 wt% of PMS having a viscosity average molecular weight of 300,000, measured as a dilute solution in diisobutylene at 20°C. Other materi¬ als referred to below are commercially available as follows: Component Manufacturer Description PPO®N640 GE Plastics Poly(2,6-dimethyl-l,4- phenylene ether) PPO®4752 GE Plastics 70/30 blend of PPO®N640 and polystyrene Kraton®-G Shell Hydrogenated styrene 1650 butadiene-styrene block copolymer Compositions of the examples were prepared by melt blending all components (including 0.5% by weight of an antioxidant) in a 0.8 inch (20 mm) Welding Engineers counter-rotating twin screw extruder fitted with two feeding zones and a strand die at the extruder exit. With respect to compositions containing zinc oxide, ground particles of the Exxpro™ polymer were predusted with zinc oxide powder prior to adding the material to the extruder mixer. The compositions were mixed and extruded over a product temperature profile of 250° to 320 °C. The extruded strands were cooled in a water bath before being pelletized into 5 x 5 mm pellets. The resulting pellets were dried to remove any surface moisture present. Mechanical tests were obtained by molding the pellets into me¬ chanical molding bars using a 15 ton Boy® injection molding machine. Tests were performed according to the following procedures. Test Test Method Tensile Strength ASTM D-638 Elongation ASTM D-638 Izod Impact strength ft-lb/in. ASTM D-638 Flexural Modulus ASTM D-790 EXAMPLE 1 A series of four different blends (A-D) having the composition shown in Table 1 were prepared as described above. Blend C (containing the Exxpro™ polymer) also contains 0.1 % by weight of zinc oxide powder based on the weight of the Exxpro™ polymer. Sample A is a control containing no added polymer modifiers and samples B-D contain 20 % by weight of the modifying polymers indicated in Table 1. Table 1. Blends with PPE as the matrix. Room temperature, 1/8" specimens. Composition A shows the properties of PPE control (PPO® N640), which has a room temperature Izod impact strength of 0.6 ft- lb/in. Both the XP-50 and Exxpro™ modified PPE compositions exhib¬ ited improved Izod impact properties when compared to the control composition A. Exxpro ™ elastomer modified PPE (Composition C) has a notched Izod impact strength of 9.2 ft-lb/in, which is a further im¬ provement over the XP-50 elastomer modified PPE (Composition B, 5.6 ft-lb/in), demonstrating the importance of the benzyl bromide func¬ tional group. The PPE/Exxpro™ blend is also tougher than PPE/Kraton®6-1650 blend (Composition D, 8.5 ft-lb/in). Furthermore, PPE/Exxpro™ blend has higher flexural modulus and tensile strength than both PPE/XP-50 and PPE/Kraton®G-1650 blends. Also, since the latter contains 33 wt.% polystyrene (PS) in block form while Exxpro™ elastomer contains no plastic segment, if Kraton®G-1650 and Exxpro™ elastomers were compared on a net rubber content basis, use of the former would likely lead to even lower stiffness and impact strength. EXAMPLE 2 Four additional blends were prepared as in Example 1 above ex¬ cept that the PPE material used was a pre-blend of PPE and polysty¬ rene (PS). As in the case of blend C above, blend G also contains 0.1% by weight of zinc oxide, based on the weight of the Exxpro™ polymer. Formulations and test data are shown in Table 2. Table 2. Blends with PPE/PS 70/30 blend as the matrix. Room temperature, 1/8" specimens. Due to the added polystyrene, the resulting blends E-H all have lower Izod impact strength. Both the Exxpro™ and XP-50 modified PPE compositions exhibited improved impact properties compared with the control. Exxpro™ elastomer modified PPE (Composition G) has a notched Izod impact strength of 2.7 ft-lb/in, which is a further im¬ provement over XP-50 elastomer modified PPE (Composition F,1.4 ft- lb/in), demonstrating again the importance of benzyl bromide func¬ tional group. PPE/Exxpro™ blend has a little lower notched Izod than PPE/Kraton®G-1650 blend (Composition H, 3.0 ft-lb/in). Again, PPE/Exxpro™ blend has higher flexural modulus and tensile strength than both PPE/XP-50 and PPE/Kraton®G-1650 blends. EXAMPLE ,3 Four additional blends (I-L) were prepared containing varying amounts of the Exxpro™ elastomer. Composition and mechanical property data for these blends are compared with blends C and G as prepared above in Table 3. As in the case of the above Exxpro™ based blends, the compositions all contain 0.1% by weight zinc oxide based on the weight of the Exxpro™ polymer. Results show an enhancement in impact properties as the level of Exxpro™ elastomer is increased in the 10-20 % range. Table 3. Blends containing different amounts of Exxnrc >™ elastomer. * Room temperature, 1/8" specimens.

Claims: CLAIMS What is claimed is: 1. A thermoplastic polymer composition comprising a blend of: a) a poly(phenylene ether) polymer; and b) an interpolymer of a C 4 -C 7 isomonoolefin containing from about 0.5 to about 20 mole% of copolymerized para-alkylstyrene. 2. The composition of claim 1 wherein said composition contains from about 1 to about 100 parts by weight of said interpolymer per 100 parts by weight of said poly(phenylene ether). 3. The composition of claim 1 wherein said isomonoolefin is isobu¬ tylene and said para-alkylstyrene is para-methylstyrene. 4. The composition of claim 1 wherein said interpolymer is a poly¬ mer of isobutylene containing the following aromatic monomer units randomly spaced along the polymer chain: 2 . wherein R and R 1 are independently hydrogen or Cj to C 4 alkyl, and X is a functional group. 5. The composition of claim 4 wherein the X-containing monomer units comprise from about 0.5 to 60 mole% of the total content of said aromatic monomer units present in said interpolymer. 6. The composition of claim 4 wherein X is halogen. 7. The composition of claim 6 wherein R and R' are each hydrogen and X is bromine present in said interpolymer at a level of less than about 2.5 wt %. 8. The composition of claim 7 wherein bromine is present in said interpolymer at a level of from about 0.05 to about 0.75 wt %. 9. The composition of claim 2 or 7 wherein said composition con¬ tains from about 5 to about 60 parts by weight of said inter¬ polymer per 100 parts by weight of said poly(phenylene ether). 10. The composition of claim 1 wherein said polyphenylene ether comprises the structure: wherein Q is the same or different alkyl group having from 1 to 4 carbon atoms and n is a whole integer of at least 100. 11. The composition of claim 10 wherein said poly(phenylene ether) is poly(2, 6-dimethyl-l, 4-phenylene ether). 12. The composition of claim 1 or 7 further containing from about 1 to about 100 parts by weight of a vinyl aromatic polymer per 100 parts by weight of said poly(phenylene ether). 13. The composition of claim 12 wherein said vinyl aromatic poly¬ mer is polystyrene. 14. The composition of claim 6 further containing from about 0.01 to about 1.5 wt % of an electrophilic reaction promoter, based on the weight of said interpolymer present in the composition. 15. The composition of claim 14 wherein said reaction promoter is zinc oxide. 16. A process for improving the physical properties of a poly(phenylene ether) comprising forming a mixture of a poly(phenylene ether) and an interpolymer of a C 4 -C 7 iso- monoolefin containing about 0.5 to about 20 wt% of copolymer- ized para-alkylstyrene and melt mixing said mixture at a tem¬ perature in the range of from about 270° to 320 °C until a uni¬ form blend is obtained. 17. The process of claim 16 wherein said mixture contains from about 1 to about 100 parts by weight of said interpolymer per 100 parts by weight of said polyphenylene ether). 18. The process of claims 17 wherein said interpolymer is a bromi- nated polymer of isobutylene and para-methylstyrene. 19. The process of claim 18 wherein said mixture further contains from about 0.01 to about 1.5 wt% of zinc oxide, based on the weight of said brominated interpolymer present in the composi- tion. 20. A shaped article prepared from the composition of claim 1 or 6. 21. The composition of claim 12 wherein the vinyl aromatic polymer is in the range of 1 to 60 parts by weight of the poly(phenylene ether).

Inventors: LI DONGMING, WANG HSIEN-CHANG, LI, DONGMING, WANG, HSIEN-CHANG
Applicants: EXXON CHEMICAL PATENTS INC, EXXON CHEMICAL PATENTS INC.
Application year: 1995
Main classification: C08L23
IPC codes: C08L71