Swelling behavior of temperature-sensitive hydrogels based on P(NIPAM-co-ADMOAB) polymers

A series of poly(N-isopropylacrylamide-co-methacryloyloxyethyl dimethyloctyl ammonium bromide) [P (NIPAM-co-ADMOAB)] hydrogels were prepared. The influences of the amount of ADMOAB in copolymeric gels on the swelling behavior were investigated. The deswelling and reswelling kinetics were also studied. Results showed that the equilibrium swelling ratios (ESRs) of copolymeric gels increased with the enhanced ADMOAB content in the composition at temperatures below LCST, and the maximum ESR was 126 compared with a value of 28 for homopolymeric gel P(NIPAM), and the ESR for all copolymeric gels tended to zero independent of the composition when the temperature was above LCST. The rate constants in deswelling process increased at first and then decreased with increasing the ADMOAB amount, and the final water retention for copolymeric gels (about 1%) was much lower than that of P(NIPAM) (20%). The swelling ratios during reswelling process increased with the ADMOAB amount, and the diffusion of water into P(NIPAM-co-ADMOAB) gels was found to be a non-Fickian mode. Though decreased in saline solutions, swelling ratios for copolymeric gels were not significantly influenced by ionic strength with NaCl concentration from 0.1 to 0.3 mol/L and higher than those of homopolymeric gels in deionized water with the same swelling time. P(NIPAM-co-ADMOAB) hydrogels can be expected as good candidates for controlled drug delivery systems and separation processes.