Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1998-07-01
2001-09-11
Wilson, Donald R. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S194000
Reexamination Certificate
active
06288171
ABSTRACT:
FIELD OF INVENTION
Thermoplastic vulcanizates from thermoplastic polypropylene and a rubber can be modified with a random propylene copolymer polymerized with single site catalyst such as metallocene catalyst. This modification typically results in an improved elongation to break and toughness.
BACKGROUND OF THE INVENTION
Thermoplastic vulcanizates are comprised of a thermoplastic phase and a crosslinked rubbery phase and desirably have the thermoplastic processing properties of the thermoplastic phase and a substantial amount of elasticity from the rubber phase. The Shore A/D hardness of a thermoplastic vulcanizate is generally controlled by the ratio of the harder thermoplastic phase to the softer rubber phase. The elongation to break of a thermoplastic vulcanizate is controlled try many factors including compatibility of the two phases, phase sizes, and added compatibilizers. It is desirable to be able to formulate a thermoplastic vulcanizate composition to have higher elongation to break and more toughness. Toughness is defined as the area under the stress strain curve when a tensile specimen of the thermoplastic vulcanizate is elongated to break.
SUMMARY OF THE INVENTION
Thermoplastic vulcanizates from a polypropylene thermoplastic phase and generally any rubber phase can be modified with random propylene copolymers polymerized with single site catalyst including metallocene catalyst to improve the physical properties of the thermoplastic vulcanizate. The random propylene copolymers can have from about 5 to about 25 weight percent of other ethylenically unsaturated monomers and more desirably from about 6 to about 20 weight percent of other ethylenically unsaturated monomers. Preferred ethylenically unsaturated monomers are ethylene or a monoolefin having from 4 to 20 carbon atoms. The residual of the random propylene copolymers is desirably repeat units derived from the polymerization of propylene. Desirable the repeat units from propylene are predominantly in either an isotactic or a syndiotactic configuration. The random propylene copolymer with crystallizable repeat units derived from propylene has a melting point above 0° C. The relative amount of the random propylene copolymer to the polypropylene thermoplastic is desirably from about 2 to about 400 parts by weight of random propylene copolymer per 100 parts by weight polypropylene thermoplastic and more desirably from about 5 to about 150 parts of random copolymer per 100 parts polypropylene thermoplastic. The propylene thermoplastic is desirably an isotactic polypropylene with a high melting temperature but can be any polypropylene other than said random copolymer. For the purpose of this specification we will distinguish between polypropylene thermoplastics which have a melting temperature of at least 120° C. and random propylene copolymer which have a melting temperature below 105. The rubbers can be traditional hydrocarbon robbers such as EPDM rubber, butyl rubber, halobutyl rubber, copolymers of p-methylstyrene and isobutylene, natural rubber, homopolymers of conjugated dienes, and copolymers of conjugated dienes or combinations thereof. Thermoplastic vulcanizates usually comprise from about 15 to about 75 parts of the thermoplastic phase and from about 25 to about 85 parts of the rubber phase based upon 100 parts total of the thermoplastic and rubber phases.
DETAILED DESCRIPTION
The random propylene copolymers used to modify the thermoplastic vulcanizates of this disclosure are copolymers of propylene with statistical insertion at least one other comonomer, other than propylene, into the polymer. Comonomers comprise ethylene and alpha-olefins having 4 to 20 carbon atoms. The arrangement of the propylene units is substantially isotactic or syndiotactic. The random propylene copolymers have narrow molecular weight distributions with a polydispersity index of less than 4. They can conveniently be prepared with single site catalyst, including metallocene catalysts, although the disclosure is not limited to those catalysts but rather to a random propylene copolymer and the thermoplastic vulcanizate composition with a random propylene copolymer. Metallocene catalyst are further described in U.S. Pat. No. 5,017,714 herein incorporated by reference for its teachings on making random propylene copolymers. The random propylene copolymers have a low level of crystallinity with a heat of fusion of less than 65 or 75 J/g.
Prior to the development of metallocene catalyst it was very difficult to prepare random propylene copolymers having narrow molecular weight distribution with a polydispersity index of less than 4 or 5 with more than about 3 or 6 weight percent of a second comonomer. Rubbery copolymers such as EPDM or EPR rubber were available. Now it is possible to prepare thermoplastic random copolymers with from about 2 to about 16 or 20 weight percent of a second comonomer or comonomers. Prior art pseudorandom propylene copolymer was made by a polymerization with a propylene feed and a second olefin feed, said second olefin generally having 2 or Hi to 8 or 12 carbon atoms, keeping a relatively constant feed ratio. The catalysts used would have several different active sites such that some sites incorporate the second olefin more efficiently than others. The different sites also can result in different polymer chain lengths. This results in a broad molecular weight distribution and a broad compositional distribution of propylene in the resulting polymer.
The random propylene copolymer of this invention desirably have a narrow compositional distribution. While not meant to be limited thereby, it is believed that the narrow composition distribution of the random propylene copolymer is important. We believe that the narrow compositional distribution is a result of using a single sited catalyst (such as metallocene) which allows only a single statistical mode of addition of ethylene and propylene. We believe this results in no statistically significant difference in the composition of the polymer among two polymer chains. The intermolecular composition distribution of the polymer is determined by thermal fractionation in a solvent. A typical solvent is a saturated hydrocarbon such as hexane or heptane. This thermal fractionation procedure is described below. Typically, approximately 75 percent by weight and more preferably 85 percent by weight of the polymer is isolated as a one or two adjacent, soluble fraction with the balance of the polymer in immediately preceding or succeeding fractions. Each of these fractions has a composition (weight percent ethylene content) with a difference of no greater than 20 weight percent (relative) of the average weight percent ethylene content of the random propylene copolymer component. The random propylene copolymer is narrow in compositional distribution if it meets the fractionation test outlined above.
In the random propylene copolymer the number and distribution of ethylene residues is consistent with the statistical polymerization of ethylene, propylene and optional amounts of diene. In stereoblock structures, the number of monomer residues of any one kind adjacent to one another is greater than predicted from a statistical distribution in random propylene copolymers with a similar composition. Historical polymers with stereoblock structure have a distribution of ethylene residues consistent with these blocky structures rather than a statistical distribution of the monomer residues in the polymer. The intramolecular composition distribution of the polymer may be determined by C-13 NMR which locates the ethylene residues in relation to the neighboring propylene residue. A statistical distribution of the ethylene and propylene sequences will result for a polymer if (1) it is made with a single sited catalyst, such as a single site metallocene catalyst, which allows only a single statistical mode of addition of ethylene and propylene and (2) it is made in a well mixed, continuous monomer feed stirred tank polymerization reactor which allows only a single polymerization mode for subs
Abdou-Sabet Sabet
Datta Sudhin
Ellul Maria D.
Finerman Terry
Gadkari Avi
Advanced Elastomer Systems L.P.
Hudak Daniel J.
Laferty Samuel
Skinner William A.
Wilson Donald R.
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