A novel monomer called 4-acetyl acryloyl ethyl acetate (AAEA) was designed and synthesized, and a series of P(AAEA-co-AA) temperature sensitive hydrogels were obtained via free radical solution copolymerization between AAEA and acrylic acid (AA). The novel monomer and the hydrogel were characterized using ¹H NMR and FT-IR spectra. The results showed that AAEA mainly existed as enol forms. In the IR spectrum of P(AAEA-co-AA), the peak of C—O stretching from enol forms of AAEA shifted to low wave numbers. This is attributed to the formation of strong hydrogen bond between PAAEA and PAA. SEM micrographs revealed that when the dosage of AAEA was high, the hydrophobic aggregation of PAAEA induced an inhomogeneous swelling of the hydrogels, and the hydrogels exhibited coarse morphology. The volume phase transition temperature (VPTT) of the hydrogels was determined by their respective DSC thermograms of swollen hydrogel specimens. The results showed that the VPTT of the hydrogels ranged from 48.2 to 61.8 ℃, and increased significantly with the decreasing dosage of AAEA. The swelling kinetics of the hydrogels was studied. The results indicate that when the dosage of AAEA was higher than 4.6 g, the hydrogel was Fick hydrogel; contrarily, the hydrogel became non-Fick hydrogel. This series of hydrogels exhibited excellent temperature sensitivity, when the temperature was lower than VPTT, the hydrogels kept at a swollen state, but when the temperature was higher than VPTT, the hydrogels deswelled significantly. Further investigation showed that the components of the hydrogels not only influenced the VPTT of the hydrogels but also influenced the temperature sensitivity of the hydrogels.

Key words: hydrogel, temperature sensitivity, swelling kinetics, volume phase transition