Alternating Copolymerization of Ethylene with Vinyl Acetate by AlEt3—ZnCl2—CCl4 Catalyst

Abstract

The behavior of the ternary catalyst system consisting of AlEt3, ZnCl2, and CCl4, which enables the copolymerization of ethylene with vinyl acetate to produce a mixture of 1: 1-alternating and random copolymers was studied. By the adoption of in-situ catalyst preparation, whereby all the catalyst components were brought into contact in the presence of the monomers, the copolymerization product gained both in yield and in molecular weight. This was ascribable, by thin-layer chromatography analysis, to the increase in the yield and molecular weight on the part of the 1: 1-alternating copolymer. Varying the feed order of the catalyst components suggested that a bimetallic complex was formed between AlEt3 and ZnCl2, and that the complex so formed made an important contribution to the alternating copolymerization. The 1: 1-alternating copolymer was formed with excellent selectivity by the procedure of aging the mixture of AlEt3 with ZnCl2 prior to the addition of CCl4. IR and NMR analyses further suggested that the bimetallic complex possibly has the ethyl group in a bridge across the aluminum and zinc atoms, and that vinyl acetate coordinates to the complex via not only the carbonyl group but also the carbon—carbon double bond to form a chelate structure.