Mechanistic Studies of Metathesis Polymerisations

Abstract

Three component catalysts have been used to polymerise cyclopentene by a metathesis ring-opening process. The active catalysts were generated from the reaction of WC16, with a metal alky 1 and a Lewis acid. The metal alkyl was either LiBu or PstLi and the Lewis acids A1Br, or SnCl4. The three components were either added separately to a solution of cyclopentene to form the catalyst in situ, or reacted together before the addition. Active systems were produced in all cases, except when LiBu, WC16, and SnC14, were reacted together before addition to monomer. Detailed studies of the dependence of the activity and decay of the catalyst during polymerisation have been carried out for all systems, using dilatometry as a means of studying the conversion of monomer to polymer. The optimum ratio of catalyst components was found to depend upon the combination used, and whether the components were premixed or added sequentially to the solution. When LiBu was used as the metal alkyl, an optimum molar ratio of W:Li was found to be 1:2. Under the same conditions optimum molar ratio of W:Ai was also only 1:2, whereas that of W:Sn was 1:4. This difference was ascribed to a greater ability of AlBr3 than Sncl4, to activate a metal carbene generated by the reaction of WC16, and LiBu...