Ethylene polymerization using tris(pyrazolyl)borate titanium(IV) catalyst supported in situ on MAO-modified silica

Abstract

Abstract The immobilization “in situ” of soluble catalyst TpMs*TiCl3 (1) on MAO-modified silica (4.0 wt.% Al/SiO2) yields active supported catalyst for ethylene polymerization. This supported catalyst showed activities between 132 and 461 kg of PE/mol[Ti] h atm which varies according to the nature of cocatalyst (MAO > TMA > TiBA > IPRA). Upon activation with MAO, no significant impact on the activity has been observed at 30 and 60 °C; however at higher temperature (90 °C) the activity decreases substantially as result of a partial catalyst deactivation. Studies related to the influence of the [Al]/[Ti] molar ratio using TMA as cocatalyst have shown that this supported catalyst presented higher activities using Al concentrations as low as 25:1. The viscosity-average molecular weights ( M ¯ v ) of the PE's produced with 1/SMAO-4 are strongly influenced by the Al concentration varying from 0.41 to 13.6 × 105 g/mol. Resulting polyethylenes can replicate the support morphology. The scanning electron microscopy (SEM) studies revealed that the spherical morphology of the supported catalyst is replicated in the polyethylene particles.