Production of polyisobutylene copolymers

Details Production of polyisobutylene copolymers Production of polyisobutylene copolymers

2000-10-06

2002-09-03

Teskin, Fred (Department: 1713)

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

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S135000, C526S185000, C526S210000, C526S212000, C526S214000, C526S216000, C526S221000, C526S347000, C502S152000, C502S156000, C502S169000

Reexamination Certificate

active

06444768

ABSTRACT:

FIELD OF INVENTION
The invention relates to an improved method for production of copolymers of isobutylene useful in rubber compounds.
BACKGROUND
Isobutylene-isoprene polymers have been well known since the 1930s. They have good impermeability to air and a high level of damping when stretched or compressed. These polymers are used extensively throughout the tire and pharmaceutical industries. The copolymers are made by a cationic slurry polymerization process at approximately −95° C. using a catalyst comprising a Lewis Acid and an initiator. Suitable Lewis Acids and initiators are well documented by Kennedy, J. P. and Marechal, E., “Carbocationic Polymerization”, Kreiger Publishing Company, 1991. Lewis Acids such as the aluminum alkyls and aluminum chloride are used extensively in both laboratory experiments and commercial scale production. Initiators such as water and anhydrous HCl are used extensively.
Isobutylene-para-methylstyrene (IPMS) polymers are also well known. They are made in a similar process to isobutylene-isoprene polymers using similar initiation systems and are also used in the tire and pharmaceutical industries. However, there are a number of difficulties with IPMS polymerization, as compared to isobutylene-isoprene copolymerization, and these difficulties are exacerbated by higher levels of para-methylstyrene (PMS) co-monomer. These difficulties include: instability of reaction temperatures and flash gas (reactor liquid composition); instability of Mooney viscosity control; lower than desirable conversion of monomer to product; higher than desirable warm-up rates due to rubber fouling, particularly around the reactor circulation pump; lower than desirable operability limitation on slurry concentrations; shorter reactor run lengths under comparable conditions; higher slurry viscosity under comparable conditions; and poorer and more erratic response of reactor to control parameters. Because of these difficulties it has historically been much more difficult and costly to produce IPMS copolymers than conventional isobutylene-isoprene copolymers. Currently, these undesirable process characteristics are managed by limiting throughput, PMS content, or a combination of the two.
It would be desirable to have a method for production of IPMS copolymers that reduces the magnitude of one or more of these complications, thereby reducing the current limitations on throughput and/or PMS content.
SUMMARY OF THE INVENTION
The invention relates to a new catalyst system for a continuous slurry polymerization process to produce random copolymers of one or more iso-olefin monomers and one or more para-alkylstyrene monomers. The process is carried out in an anhydrous polymerization system containing a mixture of the monomers in a polar solvent along with a Lewis acid and a stabilizing initiator. This polymerization system is capable of forming an in-situ electron pair donor using a stabilizing initiator. The stabilizing initiator according to this invention has the formula:
wherein:
R
1
is an alkyl, alkenyl, aryl, aralkyl, or aralkenyl group containing up to 30 carbon atoms but not less than 3 carbon atoms unless R
1
contains at least one olefinic unsaturation,
R
2
and R
3
are alkyl, aryl, or aralkyl groups containing up to 30 carbon atoms and can be the same or different,
X is a halogen or a carboxy, hydroxyl, or alkoxyl group, preferably a halogen, and n is a positive whole number.
DETAILED DESCRIPTION
The invention concerns a catalyst system and process for production of isoolefin copolymers containing a para-alkylstyrene comonomer. An improved catalyst system and process has been discovered which affords many unexpected advantages for commercial slurry polymerization of IPAS copolymers generally, and in particular IPMS copolymers. The invention is particularly useful in production of isoolefin-para-alkylstyrene (IPAS) copolymers having a higher PAS content, particularly isobutylene-para-methylstyrene (IPMS) copolymers having a higher PMS content (e.g. 10-20 weight percent PMS). This new catalyst system includes a Lewis acid with a new stabilizing initiator as described later in more detail.
The discussion and examples below are focused on preferred embodiments of the broad invention. In a particularly preferred embodiment, the copolymers produced contain isobutylene as the isoolefin and para-methylstyrene as the para-alkylstyrene comonomer. Discussion of these preferred embodiments should not be construed so as to limit the broad invention, which is applicable generally to copolymers of one or more isoolefin and one or more para-alkylstyrene (PAS) monomers. To the extent that our description is specific, this is done solely for the purpose of illustrating certain preferred embodiments and should not be taken as restricting the invention to these embodiments.
In accordance with the present invention applicants have discovered an improved polymerization system for copolymerizing an iso-mono-olefin having from 4 to 7 carbon atoms and para-alkylstyrene monomers. In accordance with a preferred embodiment of the invention, the process produces copolymers containing between about 80 and 99.5 wt. % of the isoolefin such as isobutylene and between about 0.5 and 20 wt. % of the para-alkylstyrene such as para-methylstyrene. In accordance with another embodiment, however, where glassy or plastic materials are being produced as well, the copolymers comprise between about 10 and 99.5 wt. % of the isoolefin, or isobutylene, and about 0.5 and 90 wt. % of the para-alkylstyrene, or para-methylstyrene.
The polymerization system of the invention contains a mixture of a Lewis acid catalyst, an initiator, and a polar solvent. The copolymerization reactor is maintained substantially free of impurities which can complex with the catalyst, the initiator, or the monomers, and the polymerization reaction is conducted under conditions to limit or avoid chain transfer and termination of the growing polymer chains. Anhydrous conditions are highly preferred and reactive impurities, such as components containing active hydrogen atoms (water, alcohol and the like) must be removed from both the monomer and solvents by techniques well-known in the art.
The polymerization reaction temperature is conveniently selected based on the target polymer molecular weight and the monomer to be polymerized as well as standard process variable and economic considerations, e.g., rate, temperature control, etc. The temperature for the polymerization is between −10° C. and the freezing point of the polymerization system, preferably from −25° C. to −120° C., more preferably from −40° C. to −100° C., depending on polymer molecular weight. Reaction pressure will typically be about 200 kPa to about 1600 kPa, more typically about 300 kPa to about 1200 kPa, and preferably about 400 kPa to about 1000 kPa. In order to avoid moisture condensation the reaction should be carried out under a dry inert gas atmosphere, preferably carbon dioxide or nitrogen gas, or with a liquid seal.
Isomonoolefin and PAS, particularly isobutylene and PMS, are readily copolymerized under cationic conditions. The copolymerization is carried out by means of a Lewis Acid catalyst. Suitable Lewis Acid catalysts (including Friedel-Crafts catalysts) for the process according to the present invention thus include those which show good polymerization activity with a minimum tendency to promote alkylation transfer and side reactions which can lead to branching and the production of cross-links resulting in gel-containing polymers with inferior properties. The preferred catalysts are Lewis Acids based on metals from Group IIIa, IV and V of the Periodic Table of the Elements, including boron, aluminum, gallium, indium, titanium, zirconium, tin, vanadium, arsenic, antimony, and bismuth. The preferred metals are aluminum, boron and titanium, with aluminum being the most preferred. In the practice of the method of this invention, weaker acids are preferred as they lead to less alkylation and branching and higher monomer conversion

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