Heterotactic-specific radical polymerization of N-isopropylacrylamide and phase transition behavior of aqueous solution of heterotactic poly(N-isopropylacrylamide)

Radical polymerization of N‐isopropylacrylamide (NIPAAm) in toluene at low temperatures, in the presence of fluorinated‐alcohols, produced heterotactic polymer comprising an alternating sequence of meso and racemo dyads. The heterotacticity reached 70% in triads when polymerization was carried out at −40 °C using nonafluoro‐tert‐butanol as the added alcohol. NMR analysis revealed that formation of a 1:1 complex of NIPAAm and fluorinated‐alcohol through CO···HO hydrogen bonding induces the heterotactic specificity. A mechanism for the heterotactic‐specific polymerization is proposed. Examination of the phase transition behavior of aqueous solutions of heterotactic poly(NIPAAm) revealed that the hysteresis of the phase transition between the heating and cooling cycles depended on the average length of meso dyads in poly(NIPAAm). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2539–2550, 2009 Radical polymerization of N‐isopropylacrylamide (NIPAAm) in toluene at low‐temperatures was carried out in the presence of fluorinated‐alcohols. It was found that heterotactic polymer, comprising an alternating sequence of meso and racemo dyads, was obtained. Formation of the 1:1 complex of NIPAAm and fluorinated alcohols through CO···HO hydrogen bonding is responsible for the induction of the heterotactic specificity. The phase transition behavior of heterotactic poly(NIPAAm) in aqueous solution was examined. It appeared that the hysteresis of the phase transition between heating and cooling cycles depended on the average length of meso dyad. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com.]