Abstract:The SA/P(NIPAM-co-AM) hydrogel was prepared by in situ free radical copolymerization with different content of N-isopropyl acrylamide (NIPAM) and acrylamide (AM) in sodium alginate (SA) network. By changing the composition ratio, a series of thermo-sensitive hydrogels with different lower critical solution temperature (LCST) can be prepared. And under the condition of a low AM/NIPAM ratio, the LCST of the gel is linearly correlated with the increase of the ratio. Meanwhile, the presence of carboxyl group and amino group also makes the gel responsive to pH value, which can expand the application of the hydrogels. Solid-state NMR was used to study the molecular dynamics at different temperature, especially near the LCST. When the temperature is lower than the LCST, the mobility of molecular chain is quickly, when temperature is higher than LCST, the molecular mobility decreased due to the collapse of the network. It also can be found that the mobility of different groups in different frequency do not change synchronized, but in certain sequence. The high-frequency motion of the main chain was first affected by temperature (298K), followed by high-frequency motion of the side chain (301K), and finally the low-frequency motion of the side chain (304K). The low-frequency motion of the main chain is not significantly affected by temperature. The macroscopic changes occurred after the reduction of the mobility of all the groups (305K). In addition, using the low field nuclear magnetic resonance (LF-NMR) the swelling process of composite gel was studied in situ. It was found that the diffusion of water molecules and the relaxation of macromolecular chains are synchronized, which conform to the swelling model of non-Fickian diffusion.