Synthesis, characterization and application of a novel carbon bridged half-metallocene chromium catalyst for methyl methacrylate polymerization

Abstract

A new carbon bridged cyclopentadienyl chromium complex of the type [(C₅H₄)C(CH₃)₂ CH₂(C₅H₄N)]CrCl₂ was prepared by treatment of CrCl₃·(THF)₃ in THF solution with the lithium salt of ligand containing cyclopentadienyl and pyridyl groups. The chromium complex was characterized by ¹H NMR and elemental analysis(EA), and the crystal structure was determined by X-ray diffraction analysis. Activated by Al(i-Bu)₃, the chromium complex displayed a very high activity for methyl methacrylate (MMA) polymerization. After 24 hours,more than 95.5% MMA was converted to polymethyl methacrylate (PMMA) with a viscosity average molecular weight (W _η) of 416000 g·mol⁻¹ at 60 °C for MMA/Al(i-Bu)₃/chromium catalyst molar ratio of up to 2000:20:1. Effects of temperature, molar ratios of MMA/catalyst and catalyst/cocatalyst on the polymerization have been studied. The high conversion of MMA and high molecular weight of PMMA with narrow molecular weight distribution is caused by the unique stable active site formed by the new chromium complex and aluminum cocatalyst.

Keywords

metallocene catalyst / carbon bridged half-metallocene chromium / crystal structure / MMA polymerization / PMMA

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