Phenyl-Terminated Polyolefins via Living Coordinative Chain Transfer Polymerization with ZnPh<sub>2</sub> as a Chain Transfer Agent
Mark A. Wallace, Aaron A. Burkey, Lawrence R. Sita
Abstract
Living coordinative chain transfer polymerization (LCCTP) of α-olefins, including propene, 1-hexene, 1-decene, and 4-methyl-1-pentene, using the Hf pre-initiator 1, the borate co-initiator B1, and excess equivalents of diphenylzinc (ZnPh2) as a chain transfer agent, provides excellent yields of the corresponding phenyl-terminated polyolefins with tunable degree of polymerization (DPn) and very symmetric and narrow molecular weight distribution (e.g., Đ ≤ 1.1). Reactive quenching of ZnPh2-mediated LCCTP with molecular iodine (I2) further provides orthogonally difunctionalized α-iodo, ω-phenyl polyolefins (x-PAO-Ph). The use of diethylzinc (ZnEt2) in place of ZnPh2 under otherwise identical conditions provides the corresponding ethyl-terminated polyolefin products (x-PAO-Et) with nearly the same DPn and Đ values. A mechanism is proposed for R′ group transfer from ZnR2′ and polymeryl (P) group transfer from ZnP2 during LCCTP that involves nucleophilic attack on a coordinated olefin and avoids formation of a Hf-R′ bonded intermediate. These results serve to further advance LCCTP for the production of next-generation polyolefins.