Vinyl Chloride as a Chain Transfer Agent in Olefin Polymerizations: Preparation of Highly Branched and End Functional Polyolefins

Abstract

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 β-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 β-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 Cs × 104 ∼ 30; for a propylene polymerization using a zirconocene catalyst, Cs × 104 ∼ 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.