Elastomeric propylene polymers

Details Elastomeric propylene polymers Elastomeric propylene polymers

2000-08-03

2002-07-23

Wu, David W. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S119000, C526S160000, C526S348000, C526S351000, C526S943000

Reexamination Certificate

active

06423793

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to elastomeric propylene polymers incorporating macromers and a method for the preparation of branched polymers having atactic polypropylene backbones and isotactic or syndiotactic polypropylene sidechains utilizing transition metal catalyst compounds.
BACKGROUND OF THE INVENTION
Thermoplastic elastomers have commonly been produced by forming triblock and multiblock copolymers. These types of copolymers can be useful as thermoplastic elastomer (“TPE”) compositions due to the presence of “soft” (elastomeric) blocks connecting “hard” (crystallizable or glassy) blocks. The hard blocks bind the polymer network together at typical use temperatures. However, when heated above the melt temperature or glass transition temperature of the hard block, the polymer flows readily exhibiting thermoplastic behavior. See, for example, G. Holden and N. R. Legge, Thermoplastic Elastomers: A Comprehensive Review, Oxford University Press (1987).
The best commercially known class of TPE polymers are the styrenic block copolymers (SBC), typically linear triblock polymers such as styrene-isoprene-styrene and styrene-butadiene-styrene, the latter of which when hydrogenated become essentially styrene-(ethylene-butene)-styrene block copolymers. Radial and star branched SBC copolymers are also well-known. These copolymers typically are prepared by sequential anionic polymerization or by chemical coupling of linear diblock copolymers. The glass transition temperature (T
g
) of the typical SBC TPE is equal to or less than about 80-90° C., thus presenting a limitation on the utility of these copolymers under higher temperature use conditions. See, “Structures and Properties of Block Polymers and Multiphase Polymer Systems: An Overview of Present Status and Future Potential”, S. L. Aggarwal, Sixth Biennial Manchester Polymer Symposium (UMIST Manchester, March 1976)
Insertion, or coordination, polymerization of olefins can provide economically more efficient means of providing copolymer products, both because of process efficiencies and feedstock cost differences. Thus useful TPE polymers from olefinically unsaturated monomers, such as ethylene and C
3
-C
8
&agr;-olefins, have been developed and are also well-known. Examples include the physical blends of thermoplastic olefins (“TPO”) such as polypropylene with ethylene-propylene copolymers, and similar blends wherein the ethylene-propylene, or ethylene-propylene-diolefin phase is dynamically vulcanized so as to maintain well dispersed, discrete soft phase particles in a polypropylene matrix. See, N. R. Legge, “Thermoplastic elastomer categories: a comparison of physical properties”, ELASTOMERICS, pages 14-20 (September 1991), and references cited therein.
The use of metallocene catalysts for olefin polymerization has led to additional contributions to the field. U.S. Pat. No. 5,391,629 describes thermoplastic elastomer compounds comprising tapered and block linear polymers from ethylene and alpha-olefin monomers. Polymers having hard and soft segments are said to be possible with single site metallocene catalysts that are capable of preparing both segments. Examples are provided of linear thermoplastic elastomers having hard blocks of high density polyethylene or isotactic polypropylene and soft blocks of ethylene-propylene rubber. Japanese Early Publication H4-337308(1992) describes what is said to be a polyolefin copolymer product made by polymerizing propylene first so as to form an isotactic polypropylene and then copolymerizing the polypropylene with ethylene and propylene, both polymerizations in the presence of an organoaluminum compound and a silicon-bridged, biscyclopentadienyl zirconium dihalide compound.
In addition, block-type polymers of polypropylene have been produced which exhibit elastic properties. G. Natta, in an article titled “Properties of Isotactic, Atactic, and Stereoblock Homopolymers, Random and Block Copolymers of &agr;-Olefins” (
Journal of Polymer Science,
Vol. 34, pp. 531-549, 1959) reported that an elastomeric polypropylene can be fractionated out of a polymer mixture. The elastomeric properties were attributed to a stereoblock structure comprising alternating isotactic and atactic stereosequences. Similar compositions were disclosed in U.S. Pat. No. 4,335,225. More recently, International Patent WO 95/25757 (Waymouth et al.) described a method for synthesis of elastomeric stereoblock olefin polymers using catalysts which may change their geometry (between a chiral and an achiral geometry) on a time scale that is slower than the rate of monomer insertion, but faster than the average time of a single chain construction. The resulting polymers may have properties ranging from crystalline thermoplastics to thermoplastic elastomers to amorphous gum elastomers depending on ligand type and structure, as well as polymerization conditions.
SUMMARY OF THE INVENTION
The present invention provides a thermoplastic elastomer comprising a novel structure of polypropylene. The structure combines amorphous, atactic polypropylene backbones with high melting point, low molecular weight, isotactic or syndiotactic polypropylene sidechains. This differs from the triblock or multiblock thermoplastic elastomers in that the “hard” domain is primarily present only in the sidechains. The resulting polymer is unique in that the backbone has increased elasticity over backbones having both hard and soft blocks. Also, the crystalline sidechains result in reduced chain slippage upon loading versus standard atactic polypropylene.
The thermoplastic elastomer of the present invention comprises a branched olefin polymer having crystalline sidechains and an amorphous backbone wherein at least 90 mole percent of the sidechains are isotactic or syndiotactic polypropylene and at least 80 mole percent of the backbone is atactic polypropylene.
Additionally, a process is provided for producing a thermoplastic elastomer composition comprising:
a) contacting, in solution, at a temperature from about 90° C. to about 120° C., propylene monomers with a catalyst composition comprising a chiral, stereorigid transition metal catalyst compound capable of producing isotactic or syndiotactic polypropylene;
b) copolymerizing the product of a) with propylene and, optionally, one or more copolymerizable monomers, in a polymerization reactor using an achiral transition metal catalyst capable of\ producing atactic polypropylene; and
c) recovering a branched olefin polymer.
DETAILED DESCRIPTION OF THE INVENTION
Thermoplastic elastomers contain stereoblocks of “hard” and “soft” material. In the present invention, the stereoblocks are achieved through incorporation of high melting point, low molecular weight, isotactic or syndiotactic PP macromer into amorphous, atactic PP backbones. The resulting stereoblock polymers have branch blocks with different stereo configurations in branches and backbones as compared to the polymers with stereosequences in the prior art. The highly crystalline, stereospecific branches form well dispersed domains linked by amorphous backbones. Therefore, these branch block polypropylenes have enhanced elasticity as compared to stereoblock thermoplastic elastomers, yet reduced chain slippage upon loading as compared to atactic polypropylene.
The thermoplastic elastomer compositions of this invention are comprised of branched polymers wherein both the polymer backbone and polymeric sidechains are derived from propylene polymerized under coordination or insertion conditions with activated transition metal organometallic catalyst compounds. The sidechains are isotactic or syndiotactic polypropylene which exhibit crystalline, semi-crystalline or glassy properties suitable for hard phase domains in accordance with the art understood meaning of those terms. These sidechains are attached to a polymeric backbone that is amorphous. The backbone is composed of atactic polypropylene and, optionally, one or more comonomers. Preferably, the backbone is atactic polypropylene. These compositions are useful as, among o

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