Ring-opening polymerization of cycloolefins by tungsten(VI) chloride—acetylene catalyst systems

Abstract

The ring-opening polymerization of various cycloolefins was carried out using catalytic systems for metathesis that did not contain any organometallic co-cotalysts. They were formed by the interaction of equimolar amounts of tungsten(VI) halides (WCl 6 or WOCl 4) with monosubstituted acetylenic hydrocarbons (phenyl-, n-butyl- or trimethylsilylacetylene). It was possible to enhance the activity of these systems by adding small amounts of oxygen-containing substances. The use of WCl 4-phenyl-acetylene catalyst clarified the question of polymerizability of methyl-substituted cyclopentenes. It was shown that a mixture of 3-methyl- and 4-methylcyclopentenes gave polymers having a polymethylpentenamer structure. The thermodynamic parameters of this polymerization, which has an equilibrium character, were evaluated. Reactions occurring during the interaction of WCl 6 with phenylacetylene were studied by GC-MS. The data obtained indicated that the first step in the interaction is insertion of an acetylene molecule into the WCl bond. Some considerations are suggested concerning the possible pathways for formation of metal-carbene active centres. 13C NMR study of the copolymers obtained from phenylacetylene and cyclopentene or norbornene showed that their chains included sequences with random distributions of co-monomer units. The implications of this fact for the mechanistic interrelation between the cycloolefin metathesis polymerization and the addition polymerization of acetylene are discussed.