Evidence of Quasi-Living Character of the ansa-Zirconocene/MAO catalyzed Copolymerization of Ethylene and Norbornene

The kinetics of the ethylene-norbornene copolymerization, catalyzed by rac-Et(Ind)2ZrCl2/MAO, 90%rac/10%meso-Et(4,7-Me2Ind)2ZrCl2/MAO and rac-H2C(3-tert-BuInd)2ZrCl2/MAO was followed by sampling from the reaction mixture at fixed time intervals. Catalyst activity, copolymer composition and molar mass were studied as a function of time. The polymers showed an unusually low polydispersity and a significant increase in their molar mass with time, suggesting a quasi-living polymerization.