The state of water in thermoresponsive poly(acryloyl-L-proline methyl ester) hydrogels observed by DSC and H-1-NMR relaxometry

Hydrogels that reversibly swell or shrink in water with decreasing or incre asing temperature, respectively, were obtained by gamma ray-induced polymer ization of acryloyl-L-proline methyl ester in the presence of different amo unts of a crosslinking agent. The role of water in the hydrated polymers wa s investigated by DSC and H-1-NMR relaxometry. From the curves of fusion of water determined by the former it was possible to ascertain that the amoun t of both freezing and non freezing water decreased with increasing the cro sslinker percentage and/or swelling temperature, Moreover, at the temperatu res higher than 37 degrees C, the water absorbed by the different hydrogels is mostly present as non freezing water, The H-1-NMR relaxometry study ena bled the spin-spin and spin-lattice relaxation curves to be analyzed. It wa s possible to distinguish three "populations" of protons and identify two o f them with protons of freezing and non freezing water determined by DCS, ( C) 1999 Elsevier Science Ltd. All rights reserved.