Studies of molecular weight distribution of polyolefins

Abstract Molecular weight distributions of polyethylene and ethylene-propylene copolymers prepared with Ziegler-Natta catalysts have been studied by the precipitation fractionation method. The mol. wt. distribution in polyethylene prepared in the presence of soluble catalytic system, (C 5 H 5 ) 2 TiCl 2 Al(C 2 H 5 ) 2 Cl, has been discovered to be of bimodal character; it results from existence of two types of active centres. The effects of time of polymerization, catalyst and solvent natures, and presence of propylene in the ethylene on mol. wt. distribution were investigated. The results of fractionation are correlated with the kinetic data on ethylene polymerization. The possible mechanism of ethylene polymerization in an alkyl halide medium in the presence of (C 5 H 5 ) 2 TiCl 2 Al(C 2 H 5 ) 2 Cl has been discussed with respect to the data on mol. wt. distributions.