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

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 Tcp. 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 Tcp 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.