Polyolefin block copolymers

Details Polyolefin block copolymers Polyolefin block copolymers

2002-07-30

2004-05-18

Rabago, Roberto (Department: 1713)

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

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S161000, C526S172000, C526S348000, C526S943000, C525S240000

Reexamination Certificate

active

06737487

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to block copolymers of an &agr;-olefin and a second olefin. The block copolymers are not highly isotactic, but contain isotactic sequences and have a narrow molecular weight distribution. Blends of these block copolymers are disclosed.
BACKGROUND OF THE INVENTION
Copolymers of an &agr;-olefin and a second olefin are known and are characterized as being random or block, by their molecular weight distribution, and by the stereoregularity of the monomer units. By “stereoregularity,” we mean whether the &agr;-olefin recurring units are present in the isotactic, syndiotactic or atactic configuration. These features affect copolymer processability and physical properties. Dependent upon the end use application, different properties are desirable.
Comonomer content and comonomer distribution within the polymer chain also affect copolymer properties. R. Kravchenko and R. Waymouth,
Macromolecules
31 (1998) 1, studied arylindene zirconocenes as catalysts for ethylene-propylene copolymerizations. They report random or slightly blocky incorporation of the comonomers (monomer reactivity ratio product, r
1
r
2
,=1.0−1.9) with the unbridged catalysts and alternating distribution with the bridged catalyst studied. They show a table of eighteen other catalysts previously studied in the literature. None of the thirteen metallocene catalysts gave block copolymers (r
1
r
2
varied from as low as 0.14 to as high as 1.5). Of the Ziegler-Nafta catalysts, heterogeneous titanium catalysts gave block copolymers, but these have a broad molecular weight distribution. None of the polymers had both r
1
r
2
>2.0 and narrow molecular weight distribution.
M. Galimberti et al,
Macromolecules
32 (1999) 7968, reported some ethylene-propylene block copolymers but these were completely isotactic (isotacticity index=1.0). U.S. Pat. No. 6,111,046 provides copolymers of ethylene and propylene such that the propylene sequences have an atactic structure and the copolymer is substantially amorphous. U.S. Pat. No. 5,700,896 provides a copolymer with long isotactic sequences but as a random copolymer.
U.S. Pat. No. 6,232,260 discloses the use of transition metal catalysts based upon indenoindolyl ligands. Although it is mentioned that combinations of olefins can be used, all of the examples are ethylene polymerizations or copolymerizations of ethylene with 1-butene. There is no indication that block copolymers could be formed nor is there any indication of stereochemical control.
Pending Application Ser. No. 09/859,332, filed May 17, 2001, now U.S. Pat. No. 6,541,583, discloses a process for the polymerization of propylene in the presence of a Group 3-5 transition metal catalyst that has two non-bridged indenoindolyl ligands wherein the resulting polypropylene has isotactic and atactic stereoblock sequences. No copolymers were prepared and there is no indication given that the process would be suitable for copolymerization.
Generally, copolymers that are highly isotactic (isotacticity index >0.90) are substantially crystalline. While crystallinity increases stiffness, it often decreases the elastic properties of the polymer. Conversely, copolymers that have low tacticity (isotacticity index <0.40) are usually soft and flexible but will have lower strength and may have a tacky feel. Copolymers having intermediate tacticity would retain some of the stiffness and strength of highly isotactic copolymers, but would have enhanced flexibility and a low degree of tackiness.
“Blocky” copolymers, i.e., ones that have r
1
r
2
values greater than 2.0, have the potential to be highly compatible with a wide range of other polymers, e.g., polyethylenes, polypropylenes, elastomeric polyolefins, and the like. Moreover, blocky copolymers can also have enhanced thermal properties.
Copolymers with narrow molecular weight distribution (M
w
/M
n
) are desirable because they often have improved strength and mechanical properties compared with polymers having broader M
w
/M
n
values.
Despite the considerable work done in this area, only copolymers with a maximum of two of the desired features have been available. A copolymer is needed with all three features, namely a blocky copolymer, having a narrow molecular weight distribution and stereoregularity that is not highly isotactic but contains relatively long isotactic sequences. Copolymers with all three features should have excellent elastomeric and thermoplastic-elastomeric properties (high tensile strength, high elongation, good elastic recovery) and excellent compatibility with many olefin polymers.
SUMMARY OF THE INVENTION
The invention is a block copolymer of an &agr;-olefin and a second olefin. The block copolymer has an isotacticity index of 0.40 to 0.90 and a molecular weight distribution (M
w
/M
n
) less than 6.0. In addition, the copolymer has substantial blockiness; the product of the reactivity ratios of the olefin monomers (r
1
r
2
) is greater than 2.0. Copolymers of the invention have excellent elastomeric and thermoplastic-elastomeric properties and are compatible with many olefin polymers.
Also provided are a copolymerization process and blends of the polyolefin block copolymer with a second polymer. The copolymerization process is done in the presence of an activator and a Group 3-5 transition metal catalyst that has two non-bridged indenoindolyl ligands.
DETAILED DESCRIPTION OF THE INVENTION
Suitable &agr;-olefins for the copolymerization are C
3
-C
20
&agr;-olefins such as propylene, 1-butene, 1-hexene and 1-octene. Preferred &agr;-olefins are propylene, 1-butene, 1-hexene and 1-octene. Particularly preferred is propylene. The second olefin is different from the first. Suitable second olefins are C
2
-C
20
&agr;-olefins, such as ethylene, propylene, 1-butene, 1-hexene, 1-octene. Preferred second olefins are ethylene, propylene, 1-butene, 1-hexene and 1-octene. Particularly preferred is ethylene. A preferred combination of an &agr;-olefin and a second olefin is propylene and ethylene. A third olefin may be used. Suitable third olefins are C
2
-C
20
&agr;-olefins, such as ethylene, propylene, 1-butene, 1-hexene, 1-octene and non-conjugated dienes such as 1,5-hexadiene and 2,5-norbornylene. Preferably, the block copolymer comprises more than 60 mole % propylene units and more preferably more than 80 mole % propylene units.
The tacticity of a polymer or copolymer affects its properties. The term “tacticity” refers to the stereochemical configuration of the polymer. For example, adjacent monomer units can have either like or opposite configuration. If all monomer units have like configuration, the polymer is “isotactic.” If adjacent monomer units have opposite configuration and this alternating configuration continues along the entire polymer chain, the polymer is “syndiotactic.” If the configuration of monomer units is random, the polymer is “atactic.” When two contiguous monomer units, a “diad,” have the same configuration, the diad is called isotactic or “meso” (m). When the monomer units have opposite configuration, the diad is called “racemic” (r). For three adjacent monomer units, a “triad,” there are three possibilities. If the three adjacent monomer units have the same configuration, the triad is designated mm. An rr triad has the middle monomer unit having an opposite configuration from either neighbor. If two adjacent monomer units have the same configuration and it is different from the third monomer, the triad is designated as having mr tacticity. The configuration can be determined by
13
C nuclear magnetic resonance spectroscopy as described in
Macromolecules
6 (1973) 925 and references cited therein, and in PCT Int. Appl. WO 00/01745. For more information on polymer stereochemistry, see G. Odian,
Principles of Polymerization
, 2
nd
edition (1981), pages 568-580.
The configuration of the monomer units affects polymer properties. For example, highly isotactic polypropylene readily forms a crystalline structure and has excellent chemical and heat resistance. Unlike isotactic polyp

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