Effects of chemical composition and stereoregularity on phase-transition behaviors of aqueous solutions of copolymers composed of N-isopropylacrylamide and N-n-propylacrylamide

Radical copolymerizations of N-isopropylacrylamide (NIPAAm) and N-n-propylacrylamide (NNPAAm) in various ratios were carried out in toluene at −40 °C in the presence of 3-methyl-3-pentanol to prepare syndiotactic copolymers with racemo dyad contents of ca. 70%. It was revealed that copolymers containing more than 92.5 mol% NNPAAm units exhibited large phase-transition hysteresis of their aqueous solutions. Sequence analysis suggested that intramolecular hydrogen-bonding of contiguous NNPAAm units in syndiotactic stereosequences in the dehydrated state were responsible for induction of the large hysteresis.