Copolymerization of Vinyl Chloride with Ethylene by Ziegler-Natta Catalysts

Abstract

Abstract The copolymerization of vinyl chloride with ethylene by various Ziegler-Natta catalysts was carried out in hydrocarbon solvents at 50°C. On the basis of infrared and NMR spectroscopies of the copolymerization products, it was found that the catalyst systems consisting of Ti(O-n-Bu)4 and alkylaluminums can copolymerize vinyl chloride with ethylene, whereas those consisting of VCl4, VOCl3, Cr(acac)3, Mn(acac)3, or Co(acac)3 and alkylaluminums give polyethylene or a mixture of polyvinyl chloride and polyethylene, and are otherwise inactive. Random copolymers were easily obtained by the use of the Ti(O-n-Bu)4-AlEt2Cl and Ti-(O-n-Bu)4-AlEtCl2 catalyst systems. However, with these catalyst systems, polyethylene was obtained, along with a random copolymer, at a high ethylene feed ratio. This fact indicates the existence of two kinds of active sites, responsible to the copolymerization and the ethylene polymerization respectively. The monomer reactivity ratios were found to be r1(vinyl chloride)=2.0 and r2(ethylene)=0.2 for the copolymerization by either the Ti(O-n-Bu)4-AlEt2Cl or the Ti-(O-n-Bu)4-AlEtCl2 catalyst system. The monomer reactivity ratios are not in agreement with those found in the conventional radical copolymerization. Though the copolymerization reaction was completely inhibited upon the addition of radical inhibitors, this does not seem to support a radical polymerization mechanism directly.