Light-mediated olefin coordination polymerization and photoswitches

Polyolefins are of paramount polymeric materials in plastics industry. While classical Ziegler-Natta catalysts are still taking a superior position in global polyolefin production, it is challenging to control polymerization behaviors due to their intrinsic heterogeneity. A significant number of molecular olefin polymerization catalysts based on transition metals are capable of harnessing polymerization behaviors thanks to finely-tunable ligand sets, where the ligand variation acts as electronic and/or steric factors to the active metal center. Light has been utilized as a green and specific stimulus in the context of coordination olefin polymerization to mainly alter the electronic state of active catalytic sites, which enables photo-controlled chain propagation. A handful examples of polymerization catalytic systems having precise controllability under photo-irradiation have been developed to provide a broad range of polyolefins in terms of polymeric (micro)structure. In this Review, we wish to outline the photo-responsive, transition metal-based coordination polymerization catalysts ranging from homogeneous to heterogeneous, and monometallic to bimetallic regimes. Specific, but varied roles of light depending on the employed catalysts for olefin polymerization are presented with a strong emphasis on the photo-altered property of active species.