Chemistry and Mechanism of Alkene Polymerization Reactions with Metallocene Catalysts

Abstract

AbstractThe structures of oligomers formed in ethylene polymerization reactions catalyzed by metallocene complexes are described. Ethylene was homopolymerized and copolymerized with four 1‐alkenes—propene, hex‐1‐ene, hept‐1‐ene, and 3,3‐dimethylbut‐1‐ene—using as catalysts (n‐Bu‐Cp)2ZrCl2 and (Me‐Cp)2ZrCl2 complexes activated with MAO, both in the absence and in the presence of H2. Oligomers generated in these reactions are the low molecular weight “tails” of the molecular weight distributions of the respective homopolymers and copolymers. GC analysis affords structural identification of each polymer molecule, albeit a very short one, individually. Analysis of the co‐oligomer structures provides explicit confirmation of the standard mechanisms and kinetics of chain growth and chain transfer reactions. The kinetic features include primary and secondary insertion reactions of 1‐alkene molecules into Cp2ZrC and Cp2ZrH bonds, chain transfer reactions to AlMe3, independence of chain growth rate constants on the size of polymer chains attached to active centers, etc. GC analysis also yields detailed information on an unusual feature of metallocene catalysis, namely the formation of saturated macromolecules in ethylene polymerization reactions performed in the absence of H2.magnified image