Heterotactic-Specific Radical Polymerization of N-isopropylacrylamide and Phase Transition Behavior of Aqueous Solution of Heterotactic Poly(N-isopropylacrylamide)

摘要

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 degrees 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 center dot center dot center dot 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).