Homopolymerization of ethylene and copolymerization of ethylene and 5-ethylidene-2-norbornene with the use of C2-symmetric ansa-zirconozenes catalysts of different composition

Abstract

The homopolymerization of ethylene and the copolymerization of ethylene and 5-ethylidene-2norbornene were investigated in the presence of C2-symmetric ansa-zirconozenes complexes with various types of bridges and substituents in the indenyl ligand—rac-Et(Ind)2ZrCl2 (1), rac-Et(H4Ind)2ZrCl2 (2), rac-Me2Si(Ind)2ZrCl2 (3), rac-Me2C(Ind)2ZrCl2 (4), and rac-Me2C(tert-BuInd)2ZrCl2 (5)—and with methylalumoxane as an activator. Catalyst 5, which has the Me2C bridge and the tert-Bu substituent in the indenyl ligand of zirconocene, was the most active in the homopolymerization of ethylene. Catalyst 1, which has the Et bridge, was the most active in the copolymerization of ethylene and 5-ethylidene-2-norbornene with respect to the yield of copolymer products. The introduction of the tert-Bu substituent into the ligand of zirconocene (catalyst 5) greatly slowed the incorporation of the cyclic comonomer into the polymer chain. In terms of the product of the calculated copolymerization constants, the trend of comonomer alternation was greater in the case of catalyst 1 (r 1 r 2 = 0.042) than that in the case of catalyst 3 (r 1 r 2 = 0.061). The amorphous copolymers synthesized with catalyst 1 possessed the highest glass-transition temperature.