Comprehensive high-throughput screening of photopolymerization under light intensity variation using inline NMR monitoring

Abstract

Continuous flow chemistry offers an exceptionally high degree of operational flexibility to handle photochemical transformations. Photoinduced polymerizations, such as photoiniferter reversible addition–fragmentation chain transfer (PI-RAFT), are well documented; however, detailed kinetic investigations have been hampered so far by inconsistent use of light sources and unknown incident light intensities. Here, we used automated inline NMR monitoring in a continuous flow chemistry platform combined with a variable DC power supply unit and precise control over light intensities. The PI-RAFT polymerizations of methyl, ethyl, butyl, and hydroxyethyl methacrylate showed a clear trend of increasing conversion with increasing light intensity until a saturation limit was reached, with a concomitant increase in residual polymer dispersity. Yet, when intensities are chosen appropriately, the reactions retain good livingness. Furthermore, the influence of the RAFT R-group was quantitatively studied, underpinning the importance of choosing the right RAFT agent for photoRAFT polymerization.