Ring-opening polymerization of norbornene catalysed by W(CO) 3Cl 2(AsPh 3) 2 in the presence of other olefins

Abstract

The steric course of ring-opening polymerization catalysed by W(CO) 3Cl 2(AsPh 3) 2 is strongly influenced by the presence of other cyclic or linear olefins, such as cyclooctene, cyclohexene, 1-hexene and 1,7-octadiene. The blockiness of the polymer increases linearly with the overall olefin concentration in the reaction mixture. This effect of the individual olefins is independent of whether or not they participate in the cross-metathesis reaction to a detectable extent. The results are in agreement with the existence of two major kinetically-distinct propagating metallacarbene species, one cis- and one trans-directing. Terminal olefins act as chain transfer agents. Based on polymer fractionation, 13C NMR and GC-MS studies, two more kinds of selectivity of the catalyst was found besides the increase of σ c and r c r t , of the polymer: 1. The formation, exclusively, of oligomers of a nonsymmetric structure; 2. The lack of detectable products of the homometathesis of linear chain olefins. The results are explained by the reluctance to form CH 2 carbenes and the relatively high reaction rate of propagation, chain transfer and degenerate metathesis, compared to the productive metathesis of the terminal olefins.