COMPATIBILIZED BLENDS OF POLYPROPYLENE AND POLY(PHENYLENE ETHER) POLYMERS

Abstract: Thermoplastic compositions having improved compatibility and improved mechanical properties are prepared by melt mixing a composition comprising a poly(phenylene ether), a propylene polymer such as crystalline polypropylene and an elastomeric interpolymer of a C1 to C7 isomonoolefin, e.g., isobutylene, and a para-alkylstyrene comonomer, e.g., paramethylstyrene. The interpolymer preferably contains a benzylic functional group such as halogen (bromine). The composition also may contain a styrene polymer.

Description: COMPATIBILIZEDBLENDSOF POLYPROPYLENEANDPOLY(PHENYLENEETHER)POLYMERS INVENTOR(S): Dongming Li, Hsien-Chang Wang, Albert F. Yee, and Richard C. Yeh BACKGROUND OF THE INVENTION Field of the Invention: This invention relates to compatibilized blends comprising polypropylene and poly(phenylene ether) polymers having enhanced mechanical properties. Description of Related Art: Poly(phenylene ether) (PPE) resins are well known engineering thermoplastics possessing relatively high stiffness and softening points, e.g., in excess of about 179°C (Ency. Poly. Sci. and Eng.). These polymers are useful in many applications where good mechanical properties and heat resistance 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. Binary blends comprising PPE and crystalline polypropylene (PP) demonstrate a dramatic improvement in flexural modulus and heat distortion temperature as compared with PP alone, and are more readily processible than PPE alone. However, these blends are highly incompatible such that other mechanical properties such as tensile strength, tensile strain and impact strength tend to suffer because of the poor dispersion of PPE in the PP matrix and poor adhesion of PPE to the PP matrix. The resulting blends are quite brittle regardless of the molecular weights and ductility of the individual components. Various attempts have been made to improve the compatibility of PPE PP blends. A common technique is to incorporate in such blends a minor amount of one or more compatibilizing elastomeric polymers. For example, hydrogenated sytrene-diene block copolymers have been used to compatibilize and toughen PP/PPE blends, as described in Akkapeddi and Van Buskirk (Adv. in Poly Sci, 1992, li p. 263). However, such blends exhibit little or no enhanced stiffness as compared with PP alone. JP 04068043-A similarly discloses a molding composition stated to have improved impact resistance based on a blend of PP, PPE and an elastomer which may comprise ethylene/propylene rubber, ethylene/propylene/diene rubber and/or block copolymers of butadiene and styrene. In addition, JP 04293941 -A discloses blends stated to have improved impact strength and solvent resistance based on a blend of PP, PPE and 0.5 parts by weight (per 100 PP + PPE) of brominated butyl rubber. JP 04293942-A teaches similar compositions also containing a hydrogenated polystyrene- polybutadiene-polystyrene (SEBS) block copolymer. JP 04293943-A teaches a composition comprising a blend of PP, PPE, a hydrogenated or partially hydrogenated SBS block copolymer and a halogenated (brominated) SBS block copolymer. While these and other approaches may result in PPE-based blend compositions exhibiting some improvement in mechanical properties and processability, such blends generally exhibit poor stiffness and/or modulus properties. In addition, the presence of diene unsaturation in many of these compatibilizing polymers, e.g., SBS block copolymers and/or butyl rubber, can lead to a decrease in thermal and ultraviolet stability of the resulting blends. SUMMARY OF THE INVENTION The present invention provides for thermoplastic polymer compositions having high impact strength, high heat resistance and good processability comprising a blend of: a) polypropylene; b) a poly(phenylene ether); and c) an interpolymer of a C4 to C7 isomonoolefin containing from about 0.5 to 20 mole% of copolymerized para-alkylstyrene, para-haloalkyl or mixtures of para-alkylstyrene and para-haloalkylstyrene (hereinafter isoolefin interpolymer). Preferred blends contain from about 25 to 65 wt% of propylene polymer, about 30 to 70 wt% of poly(phenylene ether) and from about 1 to 20 wt% of the isomonoolefin interpolymer, based on the polymer content of the blend. The invention also provides for a process for improving the physical properties and compatibility of compositions containing crystalline propylene polymers and poly(phenylene ether) polymers comprising melt mixing these components with from about 1 to about 20 wt%, based on polymer content, of isomonoolefin interpolymer. The isoolefin copolymer can comprise from about 0.5 to 20 mole% of copolymerized para-substituted styrene at a temperature in the range of from about 260°C to 310°C until a uniform blend is obtained. The isomonoolefin interpolymer preferably includes functionalized interpolymers prepared by replacing a portion of benzylic hydrogen with functional groups such as halogen or other functional groups mentioned hereinafter. The composition may also contain one or more additional modifier polymers such polystyrene, impact polystyrene, hydrogenated styrene/diene/styrene block copolymers and like polymers. The compatibilized compositions of this invention combine the good mechanical properties and high heat resistance of PPE polymers with the excellent processability and economy of crystalline propylene polymers thereby providing shaped articles, e.g., fibers, films and molded articles, of high impact strength, high heat resistance and improved mechanical properties. DETAILED DESCRIPTION OF THE INVENTION It has been demonstrated that isobutylene/para-methylstyrene interpolymers particularly benzylic carbon atom halogenated interpolymers, are capable of interacting with poly(phenylene ether) polymers when melt blended at high temperature, particularly in the presence of a reaction promoter such as zinc oxide, as described in copending U.S. Application S.N. 08/306,047, filed September 14, 1994. The present invention builds further on these discoveries to provide compatibilized blends comprising crystalline propylene polymer and a poly(phenylene ether) polymer having improved processability and improved mechanical properties. Poly(phenylene ether ) (PPE) thermoplastic engineering resins which are used 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 ethers) 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-l, 4- phenylene ether) and poly(2-ethyl-6-propyl-l, 4-phenylene ether). These polymers and their method of preparation are further described in U.S. Patent 3,383,435, the complete disclosure of which is incorporated herein by reference. Crystalline propylene polymers which are present as a blend component in the composition of the invention include polypropylene and crystalline copolymers of propylene with up to 20 wt% of a copolymerizable C 2 or C 4 -C 8 monoolefin, most preferably ethylene. These polymers are well known in the art and are generally prepared by polymerization of propylene or a propylene/monoolefin mixture in the presence of the so called Ziegler/Natta transition catalysts, e.g., a transition metal halide combined with a tri alkyl aluminum compound. Polypropylene can also be prepared in the presence of metallocenes and activators. Preferred propylene polymers for use in the present invention exhibit a Melt Flow Index at 230°C in the range of from about 0.1 to 100, more preferably from about 0.1 to 10. The C 4 -C 7 isoolefin interpolymers used in the invention are random elastomeric copolymers of a C 4 to C 7 isomonoolefin, such as isobutylene and a para-alkylstyrene or para-haloalkyl comonomer, preferably para-methylstyrene containing at least about 80%, more preferably at least about 90% by weight of the para-isomer, and also include functionalized inteφolymers wherein at least some of the alkyl substituent groups present in the styrene monomer units contain benzylic halogen or some other functional group. Preferred materials may be characterized as isobutylene inteφolymers containing the following monomer units randomly spaced along the polymer chain: 1. and optionally 2. wherein R and R' are independently hydrogen, lower alkyl, preferably C j to C 7 alkyl and primary or secondary alkyl halides and X is a functional group such as halogen. Preferably R and R' are each hydrogen. Up to about 60 mole% of the para-substituted styrene present in the inteφolymer structure may be the functionalized structure (2) above. Where monomer units 2 in the above formula are absent, then the isomonoolefin inteφolymer is non-functionalized, i.e., is a random copolymer of isomonoolefin and para-alkylstyrene. The most preferred of inteφolymers 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 inteφolymer is at least a teφolymer 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 incoφorated by nucleophilic substitution of benzylic halogen with the other groups such as alkoxide, phenoxide, carboxylate, thiolate, thioether, thiocarbamate, dithiocarbamate, thiourea, xanthate, cyanide, malonate, amine, amide, carbazole, phthalamide, maleimide, cyanate and mixtures thereof. These functionalized isomonoolefin inteφolymers and their method of preparation are more particularly disclosed in U.S. Patent 5,162,445, the complete disclosure of which is incoφorated herein by reference. Most useful of such functionalized materials are elastomeric random inteφolymers of isobutylene and para-methylstyrene containing 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 compositional distribution such that at least 95% by weight of the polymer has a para-alkylstyrene and para-benzylic haloalkylstyrene 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 viscosity average molecular weight in the range of from about 200,000 up to about 200,000, and a preferred number average molecular weight in the range of from about 25,000 to about 750,000, as determined by Gel Permeation Chromatography. The inteφolymers may be prepared by a slurry polymerization of the monomer mixture using a Lewis Acid catalyst, followed by halogenation, preferably bromination, in solution in the presence of halogen and a radical initiator such as heat and/or light and/or a chemical initiator. Preferred inteφolymers are brominated inteφolymers which generally contain from about 0.1 to about 5 mole% of bromomethyl groups. More preferred inteφolymers contain from about 0.05 up to about 2.5 wt% of bromine based on the weight of the inteφolymer, 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 inteφolymers, their method or 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 incoφorated herein by reference. In order to achieve a good balance between enhanced mechanical properties and processing properties, the polymer components may be blended in the range of from about 25 to 65 wt% propylene polymer (PP), about 30 to 70 wt% of poly(phenylene ether) polymer (PPE) and from about 1 to 20 wt% of the isomonoolefin inteφolymer, based on the polymer content of the blend. More preferred blends contain from about 35-55 wt% PP, 35-55 wt% of PPE and about 5-10 wt% of isomonoolefin inteφolymer, each based on the polymer content of the blend. Compatibility of the three component blend may be further enhanced where the isomonoolefin inteφolymer contains benzylic functional group such as halogen, e.g., bromine which is capable of reacting with PPE under mixing conditions. This reaction may be further promoted by inclusion of a catalyst in the formulation which will promote the electrophilic substitution reaction, such as zinc oxide, magnesium oxide, zinc bromide, ferric chloride and the like. These promotes 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 content of halogenated inteφolymer present in the composition. The melt processability of the composition may be further enhanced or controlled by optionally including a vinyl aromatic polymer or copolymer in addition to the isoolefin inteφolymer in the composition. Examples of such polymers are polystyrene, copolymers of styrene with less than 50 wt% of acrylonitrile, block copolymers of styrene with a conjugated diene such as butadiene or isoprene as well as hydrogenated or partially hydrogenated versions thereof, high impact polystyrene and mixtures thereof. A particularly preferred styrene polymer for this puφose is a hydrogenated styrene-diene-styrene block copolymer, more correctly referred to as a styrene-ethylene/butylene-styrene (SEBS) block copolymer. These styrene polymers generally have a number average molecular weight in the range of about 25,000 to 1,000,000 and may be included in the composition at a level in the range of about 1-10 wt%, based on the total polymer content of the blend. Since the isoolefin inteφolymer is quite tacky even at room temperature, it may be desirable to first form a masterbatch composition of the inteφolymer mixed with another polymer such as an olefin polymer, melt blend and extrude the mixture to form non-tacky pellets. These pellets may then be melt blended with the PPE to form one blend component of this invention. Suitable olefin polymers include one or a mixture of crystallizable polymers such as polypropylene, high density polyethylene and ethylene/propylene copolymers as well as amoφhous polymers such as low density polyethylene and copolymers of ethylene/propylene and up to 10 wt% of a non-conjugated diene such as norbornadiene, 1, 4- hexadiene, dicyclopentadiene, and the like. Generally speaking, these masterbatch pre-blends may contain from about 50 to 95 wt% of the inteφolymer and the balance one or a mixture of the olefin polymers, most preferably a crystalline propylene polymer. Tack may also be reduced by pre-dusting the inteφolymer with zinc oxide or other of the powdered reaction promoters described above. Alternatively, the blends may be prepared by combining all the polymer components under shear mixing conditions using any suitable melt mixing device such as a Banbury Mixer, or, most preferably, in a mixer/extruder. Preferred melt mixing temperatures are in the range of from about 260°C to about 310°C, more preferably from about 270°C to about 300°C, for a period of mixing time sufficient to achieve a uniform dispersion of the polymer components within the matrix polymer, usually about 0.5 to 4 minutes. In a more preferred embodiment of the invention, the blend design is such that PP serves as the matrix polymer phase and PPE forms a dispersed phase within the PP matrix. The elastomeric inteφolymer tends in turn to be evenly dispersed within the PPE dispersed phase as fine spherical particles, thereby serving to toughen the PPE dispersed phase. It is also believed that some of the inteφolymer dispersed particles may migrate to the interface between the PP and PPE phases, thereby serving to compatibilize the PP/PPE blend without migrating into the PP matrix, which could lead to a substantial loss of stiffness properties in the blend composition. 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 benzylic brominated inteφolymer of isobutylene and para-methylstyrene (PMS) containing 5 wt% PMS, 0.3 mole% of benzylically brominated PMS (measured by NMR), 0.5 wt% bromine based on the weight of the polymer (measured by X-ray fluorescence). The inteφolymer has a viscosity average molecular weight of 300,000, measured as a dilute solution in diisobutylene at 20°C. Other materials referred to below are commercially available as follows: PP - Polypropylene homopolymer available from Exxon Chemical Coφ. under the trade name Excorene PP1042, MFI = 1.9. PPE - Poly (2,6-dimethyl-l,4 phenylene ether) available from GE plastics under the trade designation PPO®-N640. SEBS - Kraton-G 1650 available from Shell TM EXXPRO - Above described brominated copolymer of isobutylene and para¬ methylstyrene available from Exxon Chemical Coφ. Binary blends of the examples containing PPE and PP were made in W/P ZSK-30 co-rotating intermeshing twin-screw extruder fitted with a strand die at the extruder exit. The compositions were mixed and extruded over a temperature profile of 260°C to 310°C. Elastomer-containing blends were prepared by first mixing the PPE and elastomer(s) in an extruder over a temperature profile of 270°C to 310°C, pelletizing the extrudate by cooling with water and then mixing the pellets with the PP in the WP extruder. All products contained about 0.5 wt% TM antioxidant and samples containing EXXPRO also contained 0.1 wt% zinc oxide, «TM based on the weight of the EXXPRO polymer. Extruded pellets were dried to remove any surface moisture. Mechanical tests were obtained by molding the pellets into mechanical 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 Notched Izod Impact Strength ASTM D-256 Flexural Modulus ASTM D-790 Heat Distortion Temp. (HDT) ASTM D-648 Example 1 A series of different formulations (B-I) and a control PP (A) were prepared by the mixing procedure - described above. These formulations had the composition as shown in Table 1. Results of mechanical property testing are also shown in Table 1. TABLE 1 nt - not tested Example is the PP control. The PP has low impact strength (<50 J/m) and low HDT. Examples B, C and D are PP/PPE binary blends used as controls. The PPE content has a strong positive effect on the flexural modulus and the heat distortion temperature, a moderate, positive effect on the tensile strength, but an adverse effect on the notched izod impact strength and the tensile strain. The blend moφhology of Example D is characterized by very large and non-uniform dispersed phases of PPE in the PP matrix, as shown by microscopic examination. Example E is a control blend of PP with PPE and SEBS. Compared with Example D containing the same amount of PPE, this example exhibits great improvement in the notched izod impact strength, and tensile elongation, but there is a great loss in stiffness. The stiffness is lower than in Example A. Example F is a blend of PP with PPE/Exxpro M blend. Compared with Example C containing the same amount of PPE, this blend exhibits much higher flexural modulus, improved tensile strain and notched Izod impact strength. Microscopic examination shows the moφhology of this blend (Example F) to be characterized by uniform dispersed phases of PPE in the PP matrix, and the PPE dispersed phases are much finer than that in control Example D. Example G incoφorates both SEBS and Exxpro in the PP/PPE blends. Compared with Examples E and F containing more PPE, this blend exhibits a notched izod impact strength similar to that for Example E, much higher than Examples C and F, but the stiffness is much higher than Example E. This blend exhibits much better toughness/stiffness balance, and its HDT is still much higher than that of PP (Example A). Microscopic examination shows the moφhology of this blend (Example G) to be characterized also by uniform dispersed phases of PPE in the PP matrix, and the PPE dispersed phases are even finer than that in Example F, demonstrating the additional compatibilization effect of SEBS block copolymer.

Claims: CLAIMS What is claimed is: 1. A thermoplastic polymer composition comprising a blend of: a) polypropylene; b) a poly(phenylene ether); and c) an inteφolymer of C -C 7 isomonoolefin containing from about 0.5 to about 20 mole% of copolymerized para-alkylstyrene. 2. The composition of claim 1 containing from about 1 to 20 wt% of said inteφolymer, based on the polymer content of said blend. The composition of claim 2 containing from about 25 to 65 wt% of said polypropylene and about 20 to 70 wt% of said poly(phenylene ether), based on the polymer content of said blend. The composition of claim 1 wherein said isomonoolefin is isobutylene and said para-alkylstyrene is para-methylstyrene. The composition of claim 1 wherein said inteφolymer is a polymer of isobutylene containing the following aromatic monomer units randomly spaced along the polymer chain: wherein R and R' are independently hydrogen, Ci to C alkyl, and primary or secondary alkyl halides and X is a functional group. 6. 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 inteφolymer. 7. The composition of claim 5 wherein X is halogen. 8. The composition of claim 7 wherein R and R' are each hydrogen and X is bromine present in said inteφolymer at a level of less than about 2.5 wt%. 9. The composition of claim 8 wherein bromine is present in said inteφolymer at a level of from about 0.05 to about 0.75 wt%. 10. The composition of claim 1 wherein said poly(phenylene ether) comprises the structure- wherein Q is the same or different alkyl group having from 1 to 14 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 further containing from about 1 to about 10 wt% of a vinyl aromatic polymer based on the total polymer content of the blend. 13. The composition of claim 12 wherein said vinyl aromatic polymer is a styrene-ethylene/butylene-styrene block copolymer. 14. The composition of claim 1 wherein said propylene polymer is a polypropylene having a Melt Flow Index at 230°C in the range of about 0.1 to 100. 15. The composition of claim 7 further containing from about 0.01 to about 1.5 wt% of an electrophilic reaction promoter, based on the weight of said inteφolymer present in the composition. 16. The composition of claim 15 wherein said reaction promoter is zinc oxide. 17. A process for preparing a compatible thermoplastic polymer blend comprising: a) forming a mixture comprising from about 25 to 65 wt% crystalline propylene polymer, from about 30 to 70 wt% of a poly(phenylene ether) polymer and from about 1 to 20 wt% of an inteφolymer of a C to C isomonoolefin containing about 0.5 to 20 mole% of copolymerized para-alkylstyrene; and b) melt mixing said mixture at a temperature in the range of about 260°C to 310°C until a uniform blend is obtained. 18. The process of claim 17 wherein said inteφolymer is a brominated polymer of isobutylene and para-methyl-styrene containing bromine at a level of from 0.05 to about 0.75 wt%. 19. The process of claim 18 wherein said poly(phenylene ether) polymer and said inteφolymer are first melt mixed at a temperature in the range of about 270°C to 320°C to form a uniform mixture, and said uniform mixture is subsequently melt mixed with said polypropylene. 20. An article prepared by heat shaping the composition of claim 1.

Inventors: LI DONGMING, WANG HSIEN-CHANG, YEE ALBERT FAN, YEH RICHARD CHENG-MING, LI, DONGMING, WANG, HSIEN-CHANG, YEE, ALBERT, FAN, YEH, RICHARD, CHENG-MING
Applicants: EXXON CHEMICAL PATENTS INC, EXXON CHEMICAL PATENTS INC.
Application year: 1996
Main classification: C08L71
IPC codes: C08L23, C08L71