Comparison of the Thermoresponsive Deswelling Kinetics of Poly(2-(2-methoxyethoxy)ethyl methacrylate) Hydrogels Prepared by ATRP and FRP

Thermoresponsive hydrogels based on 2-(2-methoxyethoxy)ethyl methacrylate (MEO2MA) were prepared by both atom transfer radical polymerization (ATRP) and conventional free radical polymerization (FRP). The lower critical solution temperature (LCST) transitions of the hydrogels prepared by the different polymerization mechanisms were compared at the macroscopic level and the molecular level. Gels prepared by ATRP swelled much more, but their macroscopic deswelling was retarded in comparison with gels prepared by FRP. This retardation was especially pronounced at higher temperatures and was attributed to the enhanced formation of skin layer in uniform gels prepared by ATRP. Variable-temperature time-lapse NMR spectroscopy showed that the rate of the dehydration of polymer chains at molecular level was much faster than macroscopic deswelling.