Fine Tuning of Catalyst Active Sites to Access Advanced Ultrahigh‐Melting Polyolefins

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Abstract
Polyolefins with melting temperatures above 200°C are rare, as their synthesis typically relies on the polymerization of highly sterically congested α‐olefins, which is challenging for both industrial Ziegler–Natta and homogeneous catalysts. Pyridylamido‐Hf complexes are molecular catalysts known for their high activity and ability to incorporate sterically demanding monomers, for example, allyltrimethylsilane (ATMS) giving isotactic poly(allyltrimethylsilane) with a melting temperature of 310°C and high turnover frequency. However, they are unable to polymerize efficiently monomers such as vinylcyclohexane (VCH) or 4,4‐dimethyl‐1‐pentene (44DMP). In this study, we report a novel synthetic strategy that enables the polymerization of such sterically challenging monomers, based on a pre‐activation of the Hf catalyst by using ATMS as ligand modifier in situ. We show that ATMS acts as an effective pre‐activator of the Hf complex, enabling controlled formation of highly active species and unlocking the polymerization of sterically demanding α‐olefins. This afforded the first synthesis of isotactic poly(4,4‐dimethyl‐1‐pentene) with an unprecedented melting temperature of 420°C, and efficient polymerization of VCH and 3‐methyl‐1‐butene. These findings demonstrate how the tuning of the pyridylamido‐Hf active species through rational choice of the activating monomer can be leveraged to expand the access to ultrahigh melting temperature polyolefins.

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