Controlling polymer dispersity using switchable RAFT agents: Unravelling the effect of the organic content and degree of polymerization

Dispersity can significantly affect material properties and related applications and as such is a significant parameter to control in polymer design. Switchable RAFT agents were recently utilized as an efficient tool to tailor polymer dispersity. In this work, we investigate the effect of the organic solvent and targeted degree of polymerization (DP) in attaining dispersity-controlled homopolymers and block copolymers. By varying the addition of acid in pure aqueous media we found that a dispersity range between 1.16 and 1.58 could be obtained while the gradual incorporation of the organic content led to broader dispersity ranges. Pleasingly, when the polymerizations were performed in aqueous media, dispersity could be efficiently controlled regardless of the targeted degree of polymerization (from DP 50 to DP 800). Instead, in mixtures containing [DMF]:[H₂O] = 4:1, dispersity could be successfully tailored only up to DP = 200 while for higher targeted DPs, a reduction in the final dispersity was not feasible. To expand the scope of our system, we subsequently exploited alternative organic solvents including DMAc, dioxane, DMSO, and ACN. While DMAc showed a side reaction attributed to the high amounts of acid employed, the other solvents successfully resulted in an efficient control over dispersity with ACN requiring the lowest amount of acid to achieve the lowest dispersity value (i.e. 2 equivalents of acid yielded Đ ∼ 1.19). Notably, the highest Đ polymers synthesized in the various solvents displayed very high end-group fidelity as characterized by mass-spectrometry and in-situ chain extensions. After establishing optimal reaction conditions, we also synthesized a range of exemplary diblock and triblock copolymers (with alternating low and high Đ) demonstrating excellent dispersity control upon subsequent block additions.