Ethylene polymerization using tris(pyrazolyl)borate titanium(IV) catalyst supported in situ on MAO-modified silica
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.
Graphical abstractThe in situ immobilization of TpMs*TiCl3 (1) on MAO-modified SiO2 is able to produce high-density polyethylenes with different properties. The viscosity-average molecular weight of the polyethylenes can be controlled by varying the [Al]/[Ti] molar ratio and temperature of polymerization. The use of TMA at low Al concentration ([Al]/[Ti] = 100) showed comparable activity to that found using MAO.Figure optionsDownload full-size imageDownload as PowerPoint slide
Journal: Applied Catalysis A: General - Volume 332, Issue 1, 1 November 2007, Pages 110–114