Synthesis and unusual volume phase transition behavior of poly(N-isopropylacrylamide)-poly(2-hydroxyethyl methacrylate) interpenetrating polymer network microgel

The poly(N-isopropylacrylamide)-poly(2-hydroxyethyl methacrylate) (PNIPAM-PHEMA) interpenetrating polymer network (IPN) microgel was synthesized for the first time. FT-IR, AFM and DLS were used to help propose the mechanism of formation of the IPN microgel. Due to the hydrogen bonds between the NIPAM and HEMA monomers, polymerization of HEMA takes place earlier inside the PNIPAM microgel than on the outside. We also focus our research on the volume phase transition temperature (VPTT) of the IPN microgels obtained at different reaction times during polymerization. Due to the incorporation of the PHEMA chains, the VPTT of the IPN microgel exhibits a decreasing trend with increasing reaction time, which is unusual for an IPN microgel.