Organic compounds -- part of the class 532-570 series – Organic compounds – Heavy metal containing
Reexamination Certificate
2000-12-29
2002-11-12
Wu, David W. (Department: 1713)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heavy metal containing
C526S160000, C526S943000, C502S152000
Reexamination Certificate
active
06479685
ABSTRACT:
TECHNICAL FIELD
This invention relates to high melting polyolefin copolymers suitable as thermoplastic elastomers and catalysts and methods for their synthesis. These olefin copolymers are characterized by low glass transition temperatures, melting points above about 90° C., high molecular weights, and a narrow composition distribution between chains. The copolymers of the invention are novel reactor blends that can be sequentially frationated into fractions of differing crystallinities, said fractions nevertheless show compositions of comonomers which differ by less than 15% from the parent reactor blend. The invention also relates to a process for producing such copolymers by utilizing an unbridged metallocene catalyst that is capable of interconverting between states with different copolymerization characteristics.
BACKGROUND
Ethylene alpha-olefin copolymers are important commercial products. These copolymers find a particularly broad range of application as elastomers. There are generally three family of elastomers made from such copolymers. One class is typified by ethylene-propylene copolymers (EPR) which are saturated compounds, optimally of low crystallinity, requiring vulcanization with free-radical generators to achieve excellent elastic properties. Another type of elastomer is typified by ethylene-propylene terpolymers (EPDM), again optimally of low crystallinity, which contain a small amount of a non-conjugated diene such as ethylidene norbornene. The residual unsaturation provided by the diene termonomomer allows for vulcanization with sulfur, which then yields excellent elastomeric properties. Yet another class is typified by ethylene-alpha olefin copolymers of narrow composition distribution which possess excellent elastomeric properties even in the absence of vulcanization. For example U.S. Pat. No. 5,278,272, to Dow describes a class of substantially linear polyolefin copolymer elastomers with narrow composition distribution and excellent processing characteristics. (These latter class of elastomers are typified for example by the EXACT
tm
and ENGAGE
tm
brand products sold commercially by Exxon and Dow, respectively.) One of the limitations of the latter class of elastomers is the low melting temperature of these materials which limits their high temperature performance.
Hence it would be extremely advantageous to industry to produce copolymers of ethylene and alpha olefins which would show both elastomeric properties in the unvulcanized state and high melting points.
THE INVENTION
Summary Objects and Advantages
It is among the objects of this invention to provide methods of production of a class of novel polyolefin copolymers with a combination of interesting and useful physical characteristics, including a molecular weight distribution, M
w
/M
n
</=10, a narrow composition distribution, </=15%, high melting point index, melting points greater than about 90° C. and elastomeric properties. It is a further object of this invention to produce a novel family of crystallizable, high-melting polyolefin copolymers having a narrow composition distribution where the melting point of the polymer is greater than about 90° C. It is a further object of this invention to produce a class of high-melting, multiblock, blend, and multiblockiblend polyolefin copolymer elastomers. These novel polymers are useful as elastomeric and/or thermoplastic materials as well as compatibilizers for other polyolefin blends.
We have unexpectedly found that it is possible to prepare high melting polyolefin elastomers of narrow composition distribution using novel unbridged metallocenes as olefin polymerization catalysts. For convenience, certain terms used throughout the specification are defined below (with “</=” or “>/=” meaning less than or equal to, or greater than or equal to):
a. “Multiblock” polymer or copolymer means a polymer comprised of multiple block sequences of monomer units where the structure or composition of a given sequence differs from that of its neighbor. Furthermore a multiblock copolymer as defined herein will contain a given sequence at least twice in every polymer chain.
b. The term “composition distribution” refers to the variation in comonomer composition between different polymer chains and can be described as a difference, in mole percent, of a given weight percent of a sample from the mean mole percent composition. The distribution need not be symmetrical around the mean; when expressed as a number, for example 15%, this shall mean the larger of the distributions from the mean.
c. As used herein, the term “elastomeric” refers to a material which tends to regain its shape upon extension, such as one which exhibits a positive power of recovery at 100, 200 and 300% elongation.
d. The term “melting point index”, also referred-to as MPI=T
m
/X
c
, means the ratio of the melting point of the copolymer, T
m
, to the mole fraction of the crystallizable component, X
c
. By crystallizable component, we mean a monomer component whose homopolymer is a crystalline polymer. The melting point is taken as a maximum in a melting endotherm, as determined by differential scanning calorimetry.
The copolymers of the present invention have the following characteristics:
(a) a mole fraction of crystallizable component X
c
from 30-99%;
(b) a molecular weight distribution M
w
/M
n
</=10; and
(c) melting points above about 90° C.;
which copolymers comprise from 0-70% by weight of an ether soluble fraction, and from 0-95% of a hexanes soluble fraction which can exhibit a melting range up to about 125° C., and from 0-95% of a hexanes insoluble fraction which can exhibit a melting range up to about 142° C.
The copolymers of the present invention in one embodiment can be characterized as reactor blends in that they can be fractionated into fractions of differing degrees of crystallinity and differing melting points. Nevertheless, the comonomer composition of the various fractions of the copolymers are within 15% of the composition of the resultant polymer product produced in the reactor.
The melting points of the copolymers of the present invention are high, typically above 90° C. and the melting point indices, T
m
/X
c
are also high, typically above 80 ° C. and preferably above 115° C. The fractions can also exhibit high melting point indices. For example, it is possible to isolate a hexanes soluble fraction from the copolymers of the present invention that exhibits a melting point as high as 115° C. and a melting point index as high as 160° C. The glass transition temperatures of the copolymers are low, typically less than −20° C. and preferably below −50° C.
The molecular weights of the polymers of the present invention can be quite high, with weight average molecular weights in excess of M
w
=1,000,000 readily obtained and molecular weights as high as 2,000,000 observed. The molecular weight distributions of the copolymers are typically M
w
/M
n
</=10, preferably M
w
/M
n
</=8 and most preferably </=6.
In one embodiment, the copolymers of the present invention exhibit useful elastomeric properties. They can be used in a variety of applications typical of amorphous or partially crystalline elastomers and as compatibilizers for copolymer blends.
While not wishing to be bound by theory, it is believed that in the process of the invention, different active species of the catalyst are in equilibrium during the construction of the copolymer chains. This is provided for in the present invention by a class of unbridged metallocenes that are capable of isomerizing between states that have different copolymerization characteristics during the polymerization process. This process can thus lead to multiblock copolymers or copolymer blends where the blocks or components of the blends have different compositions of comonomers.
One embodiment of the invention includes metallocene catalysts which are able to interconvert between states whose coordination geometries are different. Thus, the inve
Hung Joyce
Kravchenko Raisa L.
Maciejewski Petoff Jennifer
Waymouth Robert M.
Dulin, Esq. Jacques M.
Harlan R.
Innovation Law Group, Ltd.
The Board of Trustees of the Leland Standard Junior University
Wu David W.
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