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
1999-07-23
2002-11-05
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S101000, C525S477000, C525S479000, C528S015000, C528S025000, C528S031000
Reexamination Certificate
active
06476132
ABSTRACT:
FIELD OF INVENTION
Polyolefins with a pendant —SiOR, —Si(OR)
2
, or —Si(OR)
3
groups are desirable components for thermoplastic vulcanizates from a semi-crystalline polyolefin and an unsaturated rubber crosslinked via hydrosilylation. The —SiOR groups and their hydrolysis products are generally reactive with hydrosilylation crosslinking agents. The resulting reaction product can help generate the right interaction between the polyolefin phase and rubber phase to provide enhanced physical properties such as decreased compression set.
BACKGROUND OF INVENTION
Union Carbide Corporation U.S. Pat. No. 4,803,244 teaches the preparation of thermoplastic elastomers from admixing under reaction conditions an unsaturated elastomer, a thermoplastic polymer and a multifunctional organosilicon compound (hydrosilylation agent) and a catalyst capable of hydrosilylating the carbon-carbon double bonds of the unsaturated elastomer. This patent used a high level of catalyst and produced relatively low levels of completely crosslinked rubber (gel).
Sumitomo Bakelite Co. has U.S. Pat. No. 5,597,867, which teaches the components of U.S. Pat. No. 4,803,244 along with a compatibilizing agent and if necessary paraffinic oil. The compatibilizing agent generally has a component molecularly compatible with the rubber and a component molecularly compatible with the thermoplastic resin e.g. a block copolymer, a random copolymer, or a graft copolymer in which at least two monomers are polymerized.
Advanced Elastomer Systems, L.P. has a U.S. Pat. No. 5,672,660 which teaches an improved process for the preparation of thermoplastic elastomers by hydrosilylation crosslinking using a platinum containing hydrosilylation catalyst and specific unsaturated diene-containing rubbers.
The Dow Chemical Company has U.S. Pat. No. 5,741,858, which teaches silane-crosslinked molded articles of a polyolefin elastomer and a crystalline polyolefin. Generally a silane with unsaturation and a hydrolyzable group are grafted via the unsaturation to a crystalline polyolefin and to a polyolefin elastomer. Thereafter, crosslinking is accomplished by hydrolyzing any alkoxy groups and thereafter dehydrocondensation of the silanol groups.
SUMMARY OF INVENTION
A thermoplastic vulcanizate from a first semi-crystalline polyolefin, an unsaturated rubber and a second thermoplastic polyolefin having at least one pendant —OR group from a silicon atom chemically attached to the second polyolefin. The unsaturated rubber or a portion thereof is crosslinked with a hydrosilylation crosslinking agent. The second polyolefin with said pendant —OR group facilitates optimal interaction between the first polyolefin and the unsaturated rubber. R is hydrogen or an alkyl group of 1 to 8 carbon atoms. The pendant —OR group or its hydrolysis product can chemically bond with the hydrosilylation crosslinking agent. Thus, the —OR groups can function as reaction sites to bond the second polyolefin to the rubber phase via the hydrosilylation crosslinking agent. The second polyolefin (especially if it is a semi-crystallilne polyolefin such as polyethylene or polypropylene) will preferably be located in or adjacent to the semi-crystalline polyolefin. The amount of said second polyolefin is desirably from about 2 to about 25 wt % of the weight of said first polyolefin and said unsaturated rubber. The first polyolefin is desirably polypropylene and the unsaturated rubber or a portion thereof is desirably EPDM.
DETAILED DESCRIPTION OF THE INVENTION
A thermoplastic vulcanizate from a first semi-crystalline polyolefin, an alkoxysilane or silanol functionalized polymer and an unsaturated elastomer crosslinked with a hydrosilylation crosslinking agent is disclosed. The alkoxysilane or silanol functionalized polymer functions to generate the desirable extent of interaction between the semi-crystalline polyolefin and the unsaturated rubber. Said polymer is a semicrystalline polyolefin with at least one —OR including OH group pendant directly from an Si atom, which Si atom is chemically attached via one or more intermediate molecules to said second polyolefin.
Alkoxysilane or Silanol Functionalized Polyolefin
An example according to this description is Linklon™ XPM 800H from Mitsubishi. It is generally characterized as a silane grafted semi-crystalline polypropylene with about 0.01 moles of pendant Si(OR)
n
groups per 100 grams of polymer where R is C
1
-C
8
and n is from 1 to 3.
It can generally be any grafted polyolefin polymer with or without residual unsaturation e.g. polyolefins with at least 80 wt % more desirably at least 90 and preferably at least 95 wt % repeating units from a single olefin monomer, preferably monoolefin, having from 2 to 12 carbon atoms. Preferred polyolefins are copolymers with at least 80 wt % repeating units from ethylene and or propylene. The functional group grafted onto the polyolefin polymer could be any molecule with olefinic unsaturation, a silicon atom, and at least one —OR or OH group pendant to said silicon atom in the molecule. The variable R can be a hydrogen or an alkyl of 1 to 8 or 12 carbon atoms, an alkoxyalkyl of 2 to 8 carbon atoms such as methoxyethyl or an acetyl group. Examples of the molecules include:
and
where each R is as defined above. Such molecules are available from silane manufacturers and distributors such as O.S.I. Specialty Inc in Danbury, Connecticut. The amount of the grafted Si—(OR) groups is desirably from about 0.005 to about 0.1 moles per 100 g of said grafted polyolefin polymer and more desirably is from about 0.01 5 to about 0.025 moles. Such technology is taught in Japanese Patent 57012051 A2 issued Jan. 21, 1982.
The alkoxysilane or silanol functionalized polymer can also be a copolymer including repeating units from olefins and olefinically unsaturated molecules having at least one OR group pendant to a Si atom as previously described. Such copolymers desirably have at least 60, more desirably at least 70, and preferably at least 80 wt % repeating units from one or more olefins preferably monoolefins of from 2 to 8 or 12 carbon atoms. Preferably the olefins are ethylene and/or propylene. The amount of the olefinically unsaturated molecule, having at least one OR group pendant to a Si atom, incorporated in the copolymer is desirably from about 0.1 to 20 wt % and more desirably from about 0.5 to 7.5 wt % based on the weight of said polymer. Such copolymers and their preparation are described in U.S. Pat. No. 5,266,627 and the references therein which are hereby incorporated by reference.
The amount of the alkoxysilane or silanol functionalized polyolefin in the thermoplastic vulcanizate is desirably from about 0.1 or 5 to about 20 or 25 wt % and more desirably from about 1 or 5 to 15 or 20 wt % based upon the weight of said first thermoplastic polyolefin and alkoxysilane or silanol functionalized polymer.
Thermoplastic Vulcanizates
Thermoplastic elastomer compositions may be prepared by melt blending a thermoplastic resin and a rubber, until the blend is homogeneous. If a composition of vulcanized rubber in a thermoplastic matrix is desired, crosslinking agents (also referred to as curatives or vulcanizing agents) are added to the blend and crosslinking occurs during the mixing. This latter process is described as dynamic vulcanization.
A wide range of thermoplastic resins and rubbers and/or their mixtures have been used in the preparation of thermoplastic elastomers, including polypropylene, HDPE, LDPE, VLDPE, LLDPE, cyclic olefin homopolymers or copolymers as well as olefinic block copolymers, polystyrene, polyphenylene sulfide, polyphenylene oxide and ethylene propylene copolymer (EP) thermoplastics. The rubbers include ethylene propylene diene rubber (EPDM), acrylonitrile butadiene rubber (NBR) copolymers of isobutylene and divinylbenzene, and natural rubber (NR) as the elastomers. When the elastomer component is crosslinked, agents such as sulfur, peroxide, phenolics and ionic compounds are often used.
Hydrosilylation Agents
Hydrosilylation has also been disclosed as a crosslinking method in U.S.
Abdou-Sabet Sabet
Medsker Robert E.
Patel Raman
Advanced Elastomer Systems L.P.
Dawson Robert
Skinner William A.
Zimmer Marc S.
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