Tuning the LCST of PNIPAM via Random Oxidation-Sensitive Thioether Functionalities

In this work, an oxidation-responsive thioether-functionalized poly(N-isopropylacrylamide) is reported, which is synthesized via reversible-addition fragmentation transfer (RAFT) polymerization using 6-(methylthio)hexyl acrylate or 2-(methylthio)ethyl acrylate as comonomers and S-ethyl-S-(a,a-dimethyl-a-acetic acid)trithiocarbonate as RAFT agent, investigating the influence over the lower critical solution temperature (LCST) of the random thioether functionalities, prior and upon oxidation. The hydrophobic thioethers shift the LCST values of the resulting copolymers to very low temperatures, but the value could be regulated upon oxidation due to the huge increase in dipolar moment. The resulting copolymers containing hydrophilic sulfoxides show much higher LCST values, reaching a difference of up to 23 degrees C after oxidation. Results are supported by H-1 NMR, size exclusion chromatography, and turbidimetry measurements.