Copolymerization of Vinyl Chloride with Ethylene by the VO(OEt)3-Alkylaluminum Catalyst Systems

The copolymerization of vinyl chloride with ethylene was carried out in n-heptane by using the catalyst systems consisting of VO(OEt)3 and AlEt3, AlEt2Cl, or AlEtCl2 at 50°C. It was found that each of the above catalyst systems produces a random copolymer at Al/V molar ratios below 1.5; however, polyethylene is mainly obtained above the ratio of 1.5. With the VO(OEt)3/AlEt3 catalyst system, its good catalyst activity being in contrast with the inactivity of the Ti(O-n-Bu)4/AlEt3 catalyst system, the maximum catalyst activity was observed at the Al/V molar ratio of 0.5. The copolymerization rate decreased with an increase in the ethylene fraction in the monomer mixture, reaching a minimum value at a 80 mol% ethylene feed; however, the rate increased above this feed ratio with a further increase in the ethylene feed. The contamination of a copolymer with polyethylene which has been observed in the copolymerization by the Ti(O-n-Bu)4/AlEt2Cl or AlEtCl2 catalyst system was not observed in the present case. The monomer reactivity ratios for the copolymerization by the VO(OEt)3/AlEt3 catalyst system were found to be r1(vinyl chloride)=2.48 and r2(ethylene)=0.02. The reaction between VO(OEt)3 and AlEt3 was investigated by means of infrared spectroscopy and gasometry, and it was found that the average valency states of the V of the catalyst system is higher than four at the Al/V molar ratio range where a random copolymer is exclusively obtained.