Effects of tris(pentafluorophenyl)borane on the activation of a metal alkyl‐free Ni‐based catalyst in the polymerization of 1,3‐butadiene

Abstract

Abstract The activation of a metal alkyl‐free Ni‐based catalyst with B(C 6 F 5 ) 3 was investigated in the polymerization of 1,3‐butadiene. A catalyst of bis(1,5‐cyclooctadiene)nickel (Ni(COD) 2 )/B(C 6 F 5 ) 3 was found to have high catalytic activity and 1,4‐ cis stereoregularity. The catalyst was also found to provide polybutadiene having a molecular weight ( M w ) of up to 117,000, even in the absence of AlR 3 and MAO. Variations in the mol ratio of B(C 6 F 5 ) 3 to Ni affected catalytic activity, 1,4‐ cis stereoregularity, and the M w of polybutadiene, while the molecular weight distribution (MWD) of polybutadiene showed little correlation with the mol ratio of B(C 6 F 5 ) 3 to Ni. The use of other borane compounds such as B(C 6 H 5 ) 3 , BEt 3 , and BF 3 etherate in place of B(C 6 F 5 ) 3 clearly showed the two main functions of B(C 6 F 5 ) 3 in the present catalyst. The high Lewis acidity of B(C 6 F 5 ) 3 enabled it to activate catalytic complexes, thus inducing the polymerization. The steric bulkiness of B(C 6 F 5 ) 3 suppressed chain transfer reactions, contributing to the production of polybutadiene with a high M w . Kinetic studies showed that the catalyst had an induction period, possibly due to the time needed for the formation of catalytic complexes starting from Ni(COD) 2 . A plot of −ln (1− X ), where X is the fractional conversion, as a function of time resulted in a linear relationship, showing that the present catalyst system followed first‐order kinetics with respect to monomer concentration. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1164–1173, 2004