Acid-Enhanced Photoiniferter Polymerization under Visible Light.

Photoiniferter (PI) is a promising polymerization methodology, often used to overcome restrictions posed by thermal reversible addition-fragmentation chain-transfer (RAFT)  polymerization. However, in the overwhelming majority of reports, high energy UV irradiation is required to effectively trigger photolysis of RAFT agents and facilitate the polymerization, significantly limiting its potential, scope, and applicability. Although visible light PI has emerged as a highly attractive alternative, most current approaches are limited to the synthesis of lower molecular weight polymers, and typically suffer from prolonged reaction times, extended induction periods, and higher dispersities. Herein, an acid-enhanced PI RAFT polymerization is introduced that efficiently operates under visible light irradiation. The presence of small amounts of biocompatible citric acid fully eliminates the lengthy induction period by enhancing photolysis, rapidly consumes the CTA, and accelerates the reaction rate, yielding polymers with narrow molar mass distributions, near-quantitative conversions, and high end-group fidelity. Ultra-high  molecular weight polymers can also be synthesized within short timescales without compromising the control over the dispersity (Ð ~1.1). The versatility of the technique is further demonstrated through the synthesis of well-defined diblock copolymers and its compatibility to various polymer classes (i.e. acrylamides, acrylates, methacrylates), thus establishing visible-light PI as a robust tool for polymer synthesis.