Vinyl chloride as a chain transfer agent in olefin polymerizations: Preparation of highly branched and end functional polyolefins

Vinyl chloride monomer (VCM) has been employed as a chain transfer agent to yield polyolefins with one vinyl end group per chain; subsequent incorporation of these macromonomers has resulted in the formation of branched polyolefins. The use of VCM as a comonomer in transition-metal-catalyzed olefin polymerizations results in beta-chloride elimination, yielding polymers that contain vinyl end groups and a chlorinated catalyst. Through reactivation of the catalyst by advantageous MAO, or other aluminum alkyl, reinitiation of the olefin polymerization can occur; the combination of elimination and reactivation allows for VCM to behave as a chain transfer agent. The use of VCM as a chain transfer agent results in the exclusive formation of vinyl end groups (no vinylidene or internal vinyl end groups) in polyethylenes, both homopolyethylene and copolymers with octene; in propylene polymerizations, vinyl end groups are formed in addition to vinylidene end groups, the result of beta-hydride elimination which occurs even in the absence of VCM. The chain transfer constants for VCM in ethylene polymerizations for a variety of single site catalysts were determined and found to be very similar, with C-s x 10(4) similar to 30; for a propylene polymerization using a zirconocene catalyst, C-s x 10(4) similar to 700. It was further observed that the resulting macromonomers formed in the polyethylene polymerizations could be incorporated into the growing polymer chains, resulting in the formation of long chain branches.