Process for selective hydrogenation of unsaturated polymers

Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...

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5253329, 525339, C08F 804

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058147101

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BRIEF SUMMARY
The present invention relates to a method for the selective hydrogenation of unsaturated polymers which contain both carbon-carbon double bonds and aromatic rings, and to a catalyst complex for performing such hydrogenation.
Double bonds of unsaturated polymers are useful, for example, in the elastomer vulcanization process, during which inter-molecular chemical bridging takes place by means of the said unsaturated double bonds and the properties of the elastomers are improved, for example they become mechanically and chemically more durable, and technically usable rubber-like products are obtained. On the other hand, unsaturated bonds, in particular olefinic carbon-carbon double bonds, which remain or are intentionally left in the final product because of processibility or final product properties, also cause disadvantages in the polymer product. These disadvantageous properties, such as poor resistance to weather, heat or ozone, can be improved by selective hydrogenation of the olefinic double bonds of the polymer.
Polymers suitable for use in this method are preferably polymers of conjugated diolefins, in particular copolymers thereof, which have been prepared from the said diolefins and vinyl aromatic hydrocarbons. These may be random or block polymers, or combinations thereof, in which the conformation of the polymer may be linear, star-like or radial. Polymers especially suitable for the invention are butadiene-styrene block polymers. The hydrogenation products of styrene-butadiene-styrene block polymers (so-called SBS polymers) are economically considerably more valuable than the initial material, since the hydrogenated product is thermoplastic and it can be reused, which cannot be done with SBS rubber which has been bridged, i.e. vulcanized, with sulfur or peroxides.
The catalyst must be a so-called homogenous compound and not bound to a solid carrier, in order for it to have access to all parts of the polymer molecule and to be able to hydrogenate any olefinic carbon-carbon double bonds therein.
Conventionally the catalysts used in many hydrogenation reactions of diene polymers have been metals of group VIII of the Periodic Table of Elements, or compounds thereof. These include compounds of nickel, cobalt, platinum and palladium. Their use has been limited by the high price of the compounds and/or the catalysis of polymer decomposition reactions caused by their residues, so that it has been necessary to remove the catalyst residues from the hydrogenated polymer.
Often a cocatalyst is used alongside the above-mentioned compounds to promote or in some other way improve the action of the catalyst proper. Suitable compounds include the alkyl aluminum compounds disclosed in U.S. Pat. Nos. 3,696,088 and 4,107,236.
It has been observed that metallocene compounds also serve as compounds which hydrogenate polymers. Their action is quite efficient, and thus it has not always been necessary to remove their residues from the final product, and the quality of the product has not suffered. In this case, also, a cocatalyst, such as alkyl aluminum compounds, alkyl lithium compounds and Grignard reagents, are needed for promoting the action of the catalyst compound. The cocatalyst used alongside a titanocene compound, which was bis-cyclopentadienyl titanium dihalide, was, according to patent application EP 532 099, alkyl benzoate and, according to EP 471 415, alkali metal compounds, in particular alkyl-Li compounds. According to patent application EP 434 469, an SBS polymer is hydrogenated by means of zirconocene and a metal complex cocatalyst. The preparation of the metal complex, which contains Li and Al compounds, is, however, carried out by a very cumbersome and time-consuming in situ procedure.
The method according to the invention is characterized in that therein the catalyst used in the hydrogenation reaction is a new metallocene/cocatalyst complex which is formed from a complex of a metallocene and alumoxane. The metallocene component precursor used is preferably zirconocene compounds of the form (Ar).sub.

REFERENCES:
patent: 4673714 (1987-06-01), Kishimoto et al.
patent: 4876314 (1989-10-01), Hoxmeier et al.
patent: 5039755 (1991-08-01), Chamberlain et al.
patent: 5057582 (1991-10-01), Hoxmeier et al.
patent: 5204419 (1993-04-01), Tsutsui et al.
patent: 5242986 (1993-09-01), Gibler et al.
Chemical Abstracts vol. 114, 1991, p. 94,, and 39-Elastomers vol. 114, 1991, 166121, p. 95.

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