Ethylene polymerization by chromium complexes with phosphorous‐bridged bisphenoxy ligand

Abstract

Abstract Chromium catalysts combined with phosphorous‐bridged bisphenoxy ligands were found to be highly active for ethylene polymerization. The most efficient catalyst precursor among them, generated by combining bis[3‐ tert ‐butyl‐5‐methyl‐2‐hydroxyphenyl](phenyl)phosphine hydrochloride ( 1a ) and CrCl 3 (THF) 3 , was characterized. X‐ray analysis of (3‐ tert ‐butyl‐5‐methyl‐2‐phenoxy)(3‐ tert ‐butyl‐5‐methyl‐ 2‐hydroxyphenyl)(phenyl)phosphine bis(tetrahydrofuran)chromium dichloride ( 6 ), obtained by the reaction of 1a and CrCl 3 (THF) 3 in the presence of NaH, revealed a unique structure in which one phenol moiety of the bisphenol did not coordinate to the chromium center. Complex 6 showed higher activities than those observed in the in situ catalyst system. Polyethylene of various molecular weights was obtained with differing activators. The highest activity (113.5 kg mmol (cat) −1 h −1 ) was observed when TIBA/TB was used as a cocatalyst. A medium molecular weight polymer with narrow molecular weight distribution ( M w = 128,700, M w / M n = 1.8) was obtained using a 6 ‐TIBA/B(C 6 F 5 ) 3 system. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3668–3676, 2007