Styrene polymerization by nickel and titanium catalysts based on tris(pyrazolyl)borate ligands

Abstract

Styrene polymerization with a series of nickel and titanium complexes based on sterically hindered tris(pyrazolyl)borate ligands, TpMs = HB(3-mesityl-pyrazolyl)3 and TpMs* = HB(3-mesityl-pyrazolyl)2(5-mesityl-pyrazolyl) have been studied in the presence of MAO cocatalyst under various polymerization conditions. All complexes showed to be active for styrene polymerization producing almost exclusively atactic polystyrene. The catalytic activities as well as the styrene conversions with nickel complexes were higher than those with the titanium analogues. Higher activities were found at 80°C. Polystyrene properties are substantially affected by the reaction conditions such as temperature of polymerization, time, and [Al]/[M] molar ratio. The GPC results showed that the molecular weight (Mw) of the polystyrene is sensitive to the temperature of polymerization varying from 16,300 to 138,300 g mol-1. ©2008 Sociedade Brasileira de Química.