Photoswitches in Order: One-Pot Synthesis of Azobenzene Main-Chain and Segmented Copolymers

Abstract

Syntheses of multifunctional polymers aim to engineer a wide range of material properties by adjusting the composition and positioning of functional groups. While manifold syntheses of side-chain-functionalized polymers are known, synthetic protocols for main-chain-functionalized polymers are less common. This work describes a general one-pot strategy to prepare polymers containing multiple functional moieties in their main-chain, e.g., azobenzene units separated by variable oligomers. The polymerization proceeds in two steps, starting from a single azobenzene initiator and commercially available monomers (lactones and cyclic carbonates). Various main-chain-functionalized polymers were obtained with a predictable and adjustable ratio of monomer units (5-20) to photoswitchable azobenzene groups. The thermal properties of these polymers were analyzed and rationalized with regard to the parent polymers’ properties and the peculiarities arising from their segmented microstructure. Furthermore, the azobenzenes’ ability to undergo light-induced cis/trans-isomerization is confirmed. High isomerization yields of up to 90% were observed for the polymers in solution with a half-life of several days for the cis-isomers in solution. When irradiated as solid films, the azobenzenes still undergo isomerization, but the cis-isomers are less stable compared to the liquid state.