Light-Controlled Switchable Ring Opening Polymerization

Light is a fascinating source of external stimulus for the regulation of polymerization processes. In this contribution, some salicylaldimine Zn­(II) complexes bearing azobenzene moieties were prepared and characterized. Isomerization between the trans and cis forms of these complexes is achieved by exposure to light; both isomers are active in the ring-opening polymerizations of ε-caprolactone (CL), rac-lactide, trimethylene carbonate, β-oxetanone, δ-valerolactone, cyclopentadecanolide, and 5-methyl-5-propyl-1,3-dioxan-2-one but exhibit different kinetic profiles. A 6-fold reactivity difference was realized for the ring-opening polymerization of CL upon irradiation with light. The light-induced isomerization also led to reactivity discrimination between different monomers in copolymerization reactions. Reversible photoswitching between two catalytically active states provides a fascinating strategy for the control of polymerization processes, as well as the compositions of the polymers produced.