Synthesis and solution behaviour of dual light- and temperature-responsive poly(triethylene glycol-co-spiropyran) copolymers and block copolymers

Abstract

We herein report on the synthesis and characterization of materials featuring a dual-responsive copolymer segment consisting of photo-responsive spiropyran (SPA) and temperature-responsive triethylene glycol acrylate (TEGA). The copolymers contain 0–16% SPA with molecular weights ranging from 37 000 to 58 000 g mol⁻¹, and both photo- and temperature-response were investigated in aqueous media. According to UV/Vis spectroscopy, the cloud point temperature decreases from 65 °C (0% SPA) to 35 °C (16% SPA) with increasing amount of SPA moieties incorporated. The copolymer response upon irradiation with 340 and or 540 nm light was also investigated, and we could demonstrate that the switching state of the SPA moiety has a significant effect on the temperature-response of the copolymers. We further synthesised diblock terpolymers via block extension of a polystyrene macroinitiator where the hydrophilic block features similar compositions as the previously described copolymers. Self-assembly in water as selective solvent leads to the formation of micellar structures with a hydrodynamic radius of up to 100 nm. The temperature- and photo-response of these systems are comparable to the results obtained for the copolymers.