Studies on the low pressure polymerization of ethylene using catalysts containing sodium alkyls

Abstract

AbstractThe low pressure polymerization of ethylene with the use of catalysts prepared from various sodium alkyls and titanium tetrachloride was studied. Catalysts prepared from amylsodium were very active over a wide range of molar ratios of amylsodium to titanium tetrachloride (2–50); the activity decreased sharply with lower molar ratios. Rate of polymerization was found to decrease sharply, probably as a result of fusing of polyethylene particles to the catalyst surface during polymerization. Up to a pressure of about three atmospheres, the polymerization gave better yields with increase in pressure, but no increase in rate was observed on using higher pressures. Yields increased also with lowering of temperature; 0°C. gave the best yields. Molecular weight determinations showed that the polyethylenes produced had high molecular weights which did not vary over a wide range. With butylsodium, catalysts similar to those with amylsodium were formed; they showed a smaller optimum range (5–9) of molar ratios of alkyl sodium to titanium tetrachloride. Catalysts prepared from phenylsodium were much weaker, and the optimum molar ratio of phenylsodium to titanium tetrachloride, contrary to the other sodium alkyls, was found to lie at much lower molar ratios of alkyl sodium to titanium tetrachloride. Polymerizations were, in the case of phenylsodium, accompanied by an induction effect. Preliminary studies on the preparation of catalysts for the low pressure polymerization of ethylene in the presence of cyclopentadienylsodium and titanium tetrachloride were as yet not successful.