Influence of WCl 6-based catalytic systems on polypentenamer microstructure

Abstract

The microstructure of polypentenamer resulting from cyclopentene polymerization initiated by two types of WCl 6-based catalytic systems has been determined from the 13C NMR spectrum. Ternary catalysts containing organoaluminium compounds as cocatalysts ( e.g. WCl 6-epichlorohydrini-Bu 3Al) lead mostly to polypentenamers of predominant trans configuration. However the nature of the activator affects the polymer microstructure; this microstructure was correlated with the reducing ability of the organoaluminium compound and the electron donor, and the acceptor ability of the activator. In contrast, the binary catalyst containing organotin as cocatalyst (WCl 6-Ph 4Sn) yields essentially polypentenamer of mainly cis configuration at −20 °C, the cis content falling at higher temperature. Analysis of double-bond pair sequences in the polymer obtained with the above catalysts showed a non-Bemoullian distribution for cis contents greater than 30%. Determination of the oxidation states of W in the active species by ceriometric titrations indicated different valency states for the two types of catalyst; the different microstructures of the polymer were correlated with these distinct valencies of the W atom. The above results are interpreted in terms of a metallacarbene-metallacy do butane mechanism; the main stereochemical features of the ringopening polymerization of cyclopentene using the two types of catalyst are outlined. The essential role of the oxidation state of the W atom for reaction stereochemistry is pointed out.