Photoinduced Single Unit Monomer Insertion Promoted by Deep Eutectic Solvents

Abstract

This study systematically investigates the kinetics and selectivity of photoinduced reversible addition−fragmentation chain-transfer single unit monomer insertion (RAFT SUMI) reactions in different solvents. The thiocarbonylthio-based chain transfer agent (CTA) was directly activated by visible light, enabling the installation of vinyl monomers. Although the SUMI reaction provides a potential way to precisely control the sequence of oligomers, it usually suffers from a slow reaction rate and low product selectivity. We found that these challenges could be overcome by simply performing the SUMI reaction in a deep eutectic solvent composed of tetrabutylammonium chloride and ethylene glycol. When comparing to common organic solvents, acetonitrile (ACN) and dimethyl sulfoxide (DMSO), photoinduced SUMI reaction in DES exhibited a significantly enhanced reaction rate and selectivity. Nearly full conversion of the initial CTA could be achieved in only 60 min of green light irradiation under N₂-degassed conditions in DES, while 120 min was required for the reaction in ACN. Furthermore, the SUMI reaction in DES showed a high oxygen tolerance. In particular, the reaction in ACN under an open-to-air condition led to a significant degradation of CTA. On the contrary, the degradation of CTA in DES was much less pronounced. Finally, DES is applicable for a wide range of monomers and the SUMI reaction of a second building block. These findings highlight the value of DES in developing green and sequence-controlled polymerization platforms.