A CLOSER LOOK AT THE LONG-CHAIN BRANCH FORMATION IN ETHYLENE POLYMERIZATION USING METALLOCENES

摘要

Polymerization of ethylene using metallocene catalysts, particularly the constrained geometry catalysts (CGC), was studied. The main focus of the paper is on the control of chain microstructure in olefin polymerization using metallocene catalysts, particularly long chain branching in ethylene polymerization. Combined metallocene catalysts, consisting of CGC and a conventional metallocene catalyst, which only produces linear chains (linear catalyst), were used to manipulate long chain branching degree. The feasibility of this technique was verified using a mathematical model developed for the polymerization of ethylene in a semi-batch reactor using combined catalyst systems. Polymerization experiments were performed to verify the validity of the proposed technique and some of the modeling results. It was shown that by choosing a proper catalyst system and polymerization conditions chain microstructure could be tailor-made. Monte Carlo simulation was also used to study the structure and length of the branches in metallocene catalyzed ethylene polymerization. This information is essential for making any correlations between LCB degree and rheological properties.