A C-13 PST/MAS NMR-STUDY OF POLY(N-ISOPROPYLACRYLAMIDE) IN SOLUTION AND IN THE GEL PHASE

C-13 Nuclear magnetic resonance (NMR) spectra of poly(N-isopropylacrylamide) (PNiPAM) in aqueous solution and in the gel phase are measured at temperatures in the range 11.5-44-degrees-C using a ceramic rotor sealed with a rubber O-ring. In these experiments, a high resolution spectrum in the gel phase was obtained by means of the pulse saturation transfer/magic angle spinning (PST/MAS) technique and so C-13 chemical shift values for all the carbons of PNiPAM were obtained. It was found that the carbonyl and methylene C-13 chemical shifts change in a stepwise manner at about 32-degrees-C, the temperature at which gelation occurs. On the basis of these results, the structural change of PNiPAM in going from isotropic solution to the gel phase was discussed.