Study on physicochemical properties of thermosensitive hydrogels constructed using graft-copolymers of poly(N-isopropylacrylamide) and Guar gum

A copolymer, poly (N‐isopropylacrylamide)‐g‐Guar gum (PNIAAm‐g‐GG, GPNA), was synthesized using N‐isopropylacrylamide (IPAAm) and Guar gum (GG). Thermosensitive hydrogels were obtained by crosslinking GPNA with glutaraldehyde (GA). The hydrogels were pseudoplastic fluid at the temperature below lower critical solution temperature (LCST), but they were dilatant fluid at temperature above LCST. With an increase in GA, hydrogels changed from dilatant fluid to pseudoplastic fluid. The state and content of water in GPNA hydrogels were studied by differential scanning calorimetry (DSC). The results indicated the existence of freezing bound water and free water when water content of the hydrogel was more than 98.4%. The melting enthalpy of freezing bound water was higher than that of free water, but the melting temperature was lower. The content of freezing bound water was more than that of nonfreezing water. At 40°C, above the LCST of hydrogel, water loss of the GPNA hydrogel was slow at the beginning, and then became more rapid with disorganization in hydrogel structure. At 35°C below LCST of hydrogel, amount of water loss in hydrogels increased with square root of time. The drug was released slowly from the gel at 40°C, and released more rapidly at 35°C. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008