Dual thermo- and light-responsive coumarin-based copolymers with programmable cloud points

Abstract

This article deals with the design of a new class of dual-responsive coumarin-based copolymers, sensitive to temperature and light (UV and near infrared). These well-defined random copolymers, composed of triethylene glycol methyl ether methacrylate (TEGMA) and 6-bromo-4-hydroxymethyl-7-coumarinyl methacrylate (CMA), were synthesized via the reversible addition–fragmentation chain transfer (RAFT) process. The thermosensitivity of a series of random copolymers P(TEGMA-co-CMA) was evaluated via turbidimetry measurements and experiments have indicated the possibility of tuning the cloud points by varying the molar composition of the copolymers. A key advantage of incorporating the hydrophobic CMA units into the polymer feed is the presence of a photocleavable ester link between the coumarin group and the polymer backbone. This photosensitivity to UV irradiation was exploited to conveniently tune the hydrophilic/hydrophobic balance of the copolymer by forming carboxylic acid moieties along the polymer backbone, leading to an impressive increase in T_cp. Interestingly, it was also demonstrated that the irradiation time was an essential parameter to control the coumarin release rate from the copolymers and thus to tune and reprogram the T_cp of materials. Furthermore, we have validated the proof of concept that the LCST of coumarin-based copolymers could also be controlled upon NIR light (via two photon absorption), that might open the door for important biological applications.