Trials and tribulations of designing multitasking catalysts for olefin/thiophene block copolymerizations

Block copolymers containing both insulating and conducting segments have been shown to exhibit improved charge transport properties and air stability. Nevertheless, their syntheses are challenging, relying on multiple post-polymerization functionalization reactions and purifications. A simpler approach would be to synthesize the block copolymer in one pot using the same catalyst to enchain both monomers via distinct mechanisms. Such multitasking polymerization catalysts are rare, however, due to the challenges of finding a single catalyst that can mediate living, chain-growth polymerizations for each monomer under similar conditions. Herein, a diimine-ligated Ni catalyst is evaluated and optimized to produce block copolymer containing both 1-pentene and 3-hexylthiophene. The reaction mixture also contains both homopolymers, suggesting catalyst dissociation during and/or after the switch in mechanisms. Experimental and theoretical studies reveal a high energy switching step coupled with infrequent catalyst dissociation as the culprits for the low yield of copolymer. Combined, these studies highlight the challenges of identifying multitasking catalysts, and suggest that further tuning the reaction conditions (e.g., ancillary ligand structure and/or metal) is warranted for this specific copolymerization. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017