Homo- and copolymerization of ethylene at high temperature with cationic zirconocen catalysts

摘要

Homo- and copolymerization of ethylene with 1-hexene were conducted at different temperature and ethylene pressure with several zirconocenes activated with dimethylanilinium tetrakis(pentafluorophenyl)borate (Me_2PhNH (centre dot) B(C_6F_5)_4)/triisobutylaluminium (i-Bu_3Al) to study the effect of ligand structure and polymerization conditions on catalytic activity, molecular weight and chain transfer reactions. At high temperature and low ethylene pressure, rac-ethylene(bisindenyl)zirconium dichloride (rac-Et(Ind)_2ZrCl_2) activated with Me_2PhNH (centre dot) B(C_6F_5)_4/i-Bu_3Al initially gives a highly active catalyst that is rapidly deactivated. trans-Vinylene double bonds, which were not formed at low temperature, were detected in polyethylene synthesized at high temperature and low ethylene pressure. They reasonably arise from #beta#-H transfer after isomerization reaction. The molecular weight of ethylene/1-hexene copolymers decreases with increasing 1-hexene feed, followed by the formation of vinylidene end groups. This reveals that #beta#-H transfer from propagating chains containing primary inserted 1-hexene as a terminal unit is predominant. This reaction is influenced by the ligand structure. At high temperature and high ethylene pressure, trans-vinylene and vinylidene contents decrease and the vinyl content increases, indicating that the high ethylene pressure controls #beta#-H transfer after isomerization reaction.