Tacticity effects on the phase diagram for poly(N-isopropylacrylamide) in water

The tacticity effects on the phase diagram for the aqueous solution of stereocontrolled poly(N-isopropylacrylamide) (PNiPA) in water were explored. The tacticity of the polymers were represented by the diad ratio, which is determined from the methylene proton peaks of the polymer measured at 140°C. The isotactic-rich PNiPA is found to be more hydrophobic than the atactic and the shape of transmittance curve for the 1% wt aqueous solutions of PNiPA is influenced by the tacticity of PNiPA. The hydrophobic interactions among the PNiPA segments are strengthened by the stereoregularity of the polymer chain. The results show that the shape of the phase boundary curve depends upon the strength of the cooperative hydration, and the phase boundary curve shifts to lower temperature and changes from a convex downward form to concentration independent one with an increase in hydration.