Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2001-08-30
2004-03-02
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...
C526S308000, C526S280000, C526S281000, C526S284000, C526S348600, C526S348700, C526S283000, C526S337000, C526S339000
Reexamination Certificate
active
06699950
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an improved cationic polymerisation process and a catalyst system therefor.
2. Description of the Prior Art
Polymers and copolymers of isobutylene are well known in the art. In particular, copolymers of isobutylene with conjugated muitiolefin have found wide acceptance in the rubber field. These polymers are generally termed in the art butyl rubber. The preparation of butyl rubber is described in U.S. Pat. No. 2.356,128 (Thomas et al.), the contents of which are incorporated herein by reference.
The term butyl rubber as used throughout this specification is intended to encompass copolymers made from the polymerization of a reaction mixture comprising an isoolefin having from 4 to 7 carbon atoms (e.g., isobutylene) and a conjugated multiolefin having from 4 to 14 carbon atoms (e.g., isoprene). Although these copolymers arc said to contain about 0.2 to about 15% combined multiolefin, in practice the butyl rubber polymers of commerce contain from about 0.6 to about 4.5 wt % of multiolefin; more specifically from about 0.1 to about 2 mole %, the remainder of the polymer being comprised of the isoolefin component.
Efforts to prepare isoolefin-multiolefin polymers of higher unsaturation have met with varying degrees of success. Where substantially gel-free polymers have been prepared containing more than about 5% multiolefin, the polymers have been of low number average molecular weight. This has been true even where these polymers had high viscosity average molecular weights. In general, however, the products formed by prior art processes either high in gel content or low in number average molecular weight are of little utility. In order to have practical commercial utility as a synthetic butyl rubber, the isobutylene-isoprene copolymers must be substantially gel-free and have a number average molecular weight of at least 120,000.
The problem associated with the relatively low unsaturation content of conventional butyl rubber is the correspondingly low number of crosslinking sites which can bond with another rubber. Also, the crosslinking behaviour of conventional butyl rubber is different than that of other highly unsaturated rubber. These properties of conventional butyl rubber result in a weak adhesive strength which is further decreased when exposed to external shock, vibration and the like.
Thus, isobutene-cyclopentadicnc copolymer has been proposed in the prior art as an alternative to conventional butyl rubber. Isobutene-cyclopentadiene copolymer has an improved adhesive strength as well as excellent gas barrier properties, even at high degrees of unsaturation. Further, while the unsaturation of the cyclopentadiene moiety in the copolymer is susceptible to attack by ozone and the like, since the unsaturation is pendant to the polymer backbone (i.e., it does not form part of the polymer backbone), the polymer backbone remains substantially unaffected. Thus, the aging properties of a vulcanizate made from the copolymer arc excellent and its improved other characteristics make it highly desirable for use in tires.
The general problem with prior art isobutene-cyclopentadiene copolymers is in the production thereof; particularly in commercial quantities. The specific problems include one or both of the following:
(i) maintaining the stability of the cyclopentadiene co-monomer for a period sufficient to effect co-polymerization (the co-monomer is normally unstable against heat);
(ii) as the degree of unsaturation increases, there is an increase in gel formation and a decrease in the molecular weight (Mw) of the copolymer.
The latter problem can be addressed by using a conventional solution polymerization approach. See, for example, one or more of:
U.S. Pat. No. 3,808,177 (Thaler et al.);
U.S. Pat. No. 3,856,763 (Thaler et al.)
U.S. Pat. No. 4,031,300 (Thaler et al.); and
U.S. Pat. No. 4,139,695 (Thaler et al.); the contents of which are hereby incorporated by reference.
The use of a solution polymerization approach to produce an isobutene-cyclopentadiene copolymer has been criticized in International Publication Number WO 97/05181 (Youn el al.), the contents of which are hereby incorporated by reference—see, for example, page 3, line 2 to page 4, line 20 of Youn et al. Indeed, the purported point of novelty taught by Youn et al. relates to a slurry polymerization approach.
Notwithstanding the prior art solution and slurry polymerization approaches for the production of isobutene-cyclopentadiene copolymers, there is still room for improvement. Specifically, it would be desirable to have a polymerization process for the production of an isobutene-cyclopentadiene copolymer which could be used with a slurry approach to produce a low (or negligible) gel content copolymer at relatively high conversion rates of the cyclopentadiene comonomer in a shortened period of time, thus improving catalyst efficiency which is low compared to state of the art butyl polymerizations.
SUMMARY OF THE INVENTION
It is an object of the present invention to obviate or mitigate at least one of the above-identified disadvantages of the prior art.
It is another object of the present invention to provide an improved catalyst system for isoolefin copolymerization and terpolymerization.
It is another object of the present invention to provide an improved process for isoolefin copolymerization and terpolymerization.
Accordingly, in one its aspects, the present invention provides a slurry process for producing a copolymer of an isoolefin and at least one other comonomer comprising the step of polymerizing a reaction mixture comprising an isoolefin a catalyst and at least one of a cycloconjugated multiolefin and an unconjugated cyclic olefin in the presence of an activator comprising a carbo cation producing species, a silica cation producing species and mixtures thereof.
Thus, the present inventors have surprisingly and unexpectedly discovered that the use of a specific activator in this cationic polymerization process surprisingly and unexpectedly improves the process by exhibiting an improved conversion in less time while maintaining a desirable Mw. This is indeed surprising given the teachings of Kennedy et al. (
J. Macromol. Sci. Chem
. A1(6). p. 977-993 (1967), the contents of which are hereby incorporated by reference) wherein tert-butyl chloride was used as chain transfer agent and resulted in a decrease of Mw. The present process is characterized by lack of a significant decrease of Mw, especially when the process is conducted in semi-batch mode.
One of the main benefits achieved with the present invention is the conversion of the monomers over a shorter period of time and higher percent conversion than when the activator is not used. Further, one or more of the following advantages may also accrue:
1. high conversion of a second comonomer in a shortened period of time;
2. a low or negligible gel content;
3. the ability to achieve useful results at temperatures in the range of from about −110° C. to about −80° C.;
Other advantages will be apparent to those of skill in the art.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention relates to a method of preparing a copolymer of an isoolefin and at least one of a cycloconjugated multiolefin and an unconjugated cyclic olefin. Of course, those of skill in the art will recognize that the products of the present process may be at least any one of: a copolymer of an isoolefin and a cycloconjugated multiolefin; a copolymer of an isoolefin and an unconjugated cyclic olefin; a terpolymer of an isoolefin, a cycloconjugated multiolefin and an unconjugated cyclic olefin; a terpolymer of an isoolefin and two (or more) different cycloconjugated multiolefins; and a terpolymer of an isoolefin and two (or more) different unconjugated cyclic olefins.
Preferably, the copolymer has a number average molecular weight about 30,000 to about 600,000, more preferably about 50,000 to about 400,000, still more preferably about 70,000 to about 350,000 and a mole % unsaturation of
Ismeier Juergen
Kreuder Carsten
Nuyken Oskar
Bayer Aktiengesellschaft
Cheng Noland J.
Gil Joseph C.
Rabago Roberto
Seng Jennifer R.
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