Reversible Gelation and Phase Transition of Aqueous Solution of Hydrophobically Modified Poly(N‐Isopropylacrylamide)

Abstract

Abstract We investigated physical gelation and phase transition of aqueous solutions of hydrophobically modified poly(N‐isopropylacrylamide) (HM‐PNIPAAm) with stearyl acrylate (SA). Aqueous solutions of HM‐PNIPAAm form a reversible gel cross‐linked with hydrophobic aggregations of stearyl groups. The physically cross‐linked HM‐PNIPAAm gel with relatively low SA content shows a two‐step volume transition with increasing temperature. Moreover, overlapping of the reversible gel–sol transition and phase separation results in the phase diagrams of the aqueous solutions of HM‐PNIPAAm, having five distinct regions: dilute sol, gel, gel–sol, sol–sol, and condensed sol regions. The overlapping of the two different phase transitions causes the two‐step volume transition.