Dispersity Control via Solvent and Additive Effects in Photoredox-Mediated Ring-Opening Metathesis Polymerization

Having a controllable and typically narrow molecular weight distribution is a hallmark of most well-controlled polymerization techniques, including metal-mediated ring-opening metathesis polymerization (ROMP). Control in photoredox-mediated metal-free ROMP, on the other hand, has been limited to spatio-temporal, average molecular weight, and stereochemical control; targeted molecular weight distributions (quantified with dispersity, Đ) have been elusive. However, we were motivated by the relationship between Đ and elementary reaction rates in reversible deactivation radical polymerizations to explore the solution presented herein. Specifically, we have demonstrated the ability to target specific Đ values, ranging from 1.23 to 1.63, in a logical and operationally simple way: by perturbing the environment of the active chain-end through solvent and additive effects. We hypothesize that this is due to the consequent effects on the rate of chain-end deactivation combined with changes in the rate of propagation.