Control of molecular weight and chain-end group in tactic polypropylenes using chain transfer agents

The intense research interest in tactic control of metallocene-mediated propylene polymerization has provided a tremendous amount of detail regarding the mechanism of polymerization,1-4 including active site structure, the regioselectivity and stereoselectivity of propylene coordination and insertion, and the relationship between catalyst symmetry and polymer microstructure and properties. Nevertheless, chain release mechanisms, usually involving various chain transfer reactions, have received less attention. Some reports5-7 focus on the control of catalyst activity, polymer molecular weight, and saturated polymer chain-end structure by introducing hydrogen transfer agents using different metallocene catalysts.