Studies on the low pressure polymerization of propylene using catalysts containing alkali metal alkyls

Abstract

AbstractThe low pressure polymerization of propylene was investigated using catalysts prepared from alkali metal alkyls and titanium tetrachloride. In all cases the efficiency of the catalysts depended on the molecular ratio of the metal alkyl to the titanium tetrachloride. In general the polymerization conditions were similar to those for ethylene although the propylene polymerized much more slowly. With n‐butyllithium–titanium tetrachloride, optimum molecular ratios were found between 1.8–2.5, with sharp drops on both sides. With amylsodium–titanium tetrachloride the optimum extended over a wide range (5.7–15), the activity decreasing sharply with lower molecular ratios. The catalysts prepared from sodium alkyls were more active than those prepared from lithium alkyls. Increasing yield was obtained on lowering the concentration of the catalyst. Up to a pressure of about 3 atmospheres, increase in the rate of polymerization was observed with increase in pressure; above this no influence of the pressure was observed. Isotactic polymers were isolated from the polymerization products by successive fractionation of the crude polymers in acetone, ether, and isooctane which dissolved the atactic polymers. With butyllithium–titanium tetrachloride catalysts, at and above optimum ratios, the isotactic fractions were about 60%. At lower ratios there was a great increase in atactic polymers. With amylsodium–titanium tetrachloride catalysts the isotactic fractions were about 70%. Phenylsodium–titanium tetrachloride catalysts were found to be very weak in the polymerization of propylene.