Control of Molecular Weight Distribution through Photoresponsive RAFT Polymerization with a Temporal Program-Controlled System

The polymer dispersity index (PDI) is a vital metric for characterizing molecular weight distribution, significantly influencing polymer material performance. However, achieving precise control over PDI in polymer synthesis remains a substantial challenge. In this study, we introduce an approach for modifying the PDI of poly(methyl acrylate) (PMA) in switchable reversible addition-fragmentation chain transfer radical polymerizations (RAFT). The devised strategy involves the utilization of photoresponsive hexaarylbiimidazole (HABI) as a mediator, coupled with temporal programming, to cyclically deactivate and reactivate propagating radicals at distinct stages throughout the polymerization process. The precise timing of the light stimulus is facilitated through computer-controlled single-chip microcomputer technology, ensuring automatic modulation of the optical state and mitigating operational inaccuracies. By manipulating external light conditions, the PDI of PMAs can be systematically adjusted within the range of 1.80 to 2.59. Validation through successful chain-extension experiments and analysis via MALDI-TOF MS confirm the preservation of good chain-end fidelity across PMAs with varying PDIs fabricated through this methodology.