Chiral poly(aza-norbornene) derivatives with tunable tacticity and living ROMP capability

Ring-opening metathesis polymerization (ROMP) is a powerful tool to produce various polymers with diverse structures and functions, but its tacticity controllability, especially for enantio-pure monomers, is relatively unexplored. The challenge lies in both the difficulty of achieving chiral monomers and the control of head/tail regioselectivity during ROMP. We herein report the synthesis and application of a sulfonamide derivative of commercial chiral Vince lactam. The easily available monomer showed simultaneous living ROMP capability and tunable head/tail regioselectivity with commercial Ru-based catalysts. More specifically, the use of the Grubbs' III catalyst (Ru-3) gave rise to head-to-tail regioselectivity, leading to isotactic "living" polymers. In contrast, the use of cyclometalated Ru-based catalysts (Ru-4 and Ru-5) enabled the formation of head-to-head polymers, leading to syndiotactic polymers. Detailed experimental and DFT studies suggest that the regioselectivity is dominated by the chain-end-control mechanism. The precise microstructural tunability enables us to systematically investigate thermal properties, crystallinity, and dielectric properties of the hydrogenated ROMP polymers.