Studies in Metathesis Polymerisation

Abstract

The WCl6 / AliBu3 initiated polymerisation of cyclopentene has been investigated as a chain reaction and attempts have been made to study the reactions of the chain, ie initiation, propagation and termination. The reactions between alkenes and tungsten hexachloride at low molar ratios of alkene : W have been studied using spectrophotometric techniques and analysis of the products by gas chromatography. These studies showed that a series of reactions takes place between tungsten hexachloride and alkenes and that a number of species are present in the system which, on addition of aluminium alkyl, produce metathesis-active complexes. Dilatometric and calorimetric techniques have been used to study the kinetics of the reaction. Previous studies conceming the kinetics of the initiation of polymerisation were confirmed using the dilatometric technique. Comparison of the results obtained by these two techniques suggested that more than one active species was formed on the addition of aluminium triisobutyl to a solution originally containing tungsten hexachloride and cyclopentene. It is suggested that these active species produce high and low molecular weight materials independently and that the rate of production of polymer is measured dilatometrically and the overall rate of consumption of monomer calorimetrically. Polymerisations initiated by WCl6 / 2AliBuz did not reach an equilibrium conversion of monomer. Addition of a second aliquot of initiator components or oxygen re-initiated polymerisation. The termination was interpreted from kinetic data and shown to be complex. Computer simulation of the reaction indicated second order termination involving both propagating and terminated species. Studies on the role of oxygen as a catalyst activator indicated the production of a system similar in nature to WCl6 / EtOH.