A photoswitchable catalyst system for remote-controlled (co)polymerization in situ

The fundamental properties of a polymeric material are ultimately governed by its structure, which mainly relies on monomer composition and connection, topology, chain length, and polydispersity. Thus far, these structural characteristics are typically set ex situ by the specific polymerization procedure, eventually limiting the future design space for the creation of more sophisticated polymers. Herein, we report on a single photoswitchable catalyst system, which enables in situ remote control over the ring-opening polymerization of l-lactide and further allows regulation of the incorporation of trimethylene carbonate and δ-valerolactone monomers in copolymerizations. By implementing a phenol moiety into a diarylethene-type structure, we exploit light-induced keto-enol tautomerism to switch the hydrogen-bonding-mediated monomer activation reversibly ON and OFF. This general and versatile principle allows for exquisite external modulation of ground-state catalysis of a living polymerization process in a closed system by ultraviolet and visible light and should thereby facilitate the generation of new polymer structures.