Phase transition of aqueous solutions of poly(N-isopropylacrylamide) and poly(N-isopropylmethacrylamide)

Abstract

When aqueous solutions of well-fractionated poly(N-isopropylacrylamide) samples are heated, the polymer molecular dimensions change abruptly at a critical temperature (about 32°C), followed by aggregation of individual polymer chains dispersed in a state of globular particles to give an optically detectable phase transition. The transition occurs independently of either the molecular weight of the polymer (5×104 to 840×104) or its concentration (0.01 to 1 wt%). This behavior is reminiscent of the thermal denaturation of proteins in aqueous medium.