Study On Preparation And Properties Of Hydrophobically Modified PNIPA Hydrogels

Hydrophobically modified poly(N-isopropylacrylamide)(PNIPA) hydrogels were synthesized by the free micellar copolymerization in aqueous solution of N-isopropylacrylamide(NIPA) with a small amout of cross-linking agent N,N'-methylenebisacrylamide(Bis) and the hydrophobic acrylate monomer such as methyl acrylate(MA),ethyl acrylate(EA),butyl acrylate(BA) and dodecyl acrylate(DA). Interpenetrating polymer network (IPN) hydrogels were prepared by introducing polyacrylic acid (PAA) network into P(NIPA-co-EA) network. The chemical structures and microcosmic morphology of hydrogels were investigated by means of the infrared spectra, the fluorescence spectra and the scanning electron microscope etc. The properties of different structure hydrogels at different condition were studied. The relation between structure and property of hydrogels was investigated in order to prepare excellent hydrogels.Results show that microcosmic morphology and property of hydrogels depend on their chemical structure. The porosity size of hydrophobically modified PNIA hydrogel is the largest in PNIPA hydrogel, IPN hydrogel and NIPA-co-acrylate hydrogel. The porosity size of IPN hydrogel is larger than that of PNIPA hydrogel. When hydrophobically modified PNIPA hydrogel was synthesized by the free micellar copolymerization in aqueous solution, the interaction between surfactant and hydrophobic group of hydrogels network is quite strong. So it acts as porosityagent in the system and can make macroporous hydrogel. The lower critical solution temperature (LCST) of hydrophobically modified hydrogels is nearly identical to that of PNIPA. And the temperature sensitivity and mechanic strength of hydrophobically modified hydrogels are improved.The hydrogels with different structure are of different swelling behavior in the different medium; The swelling ratio of hydrophobically modified PNIPA hydrogels is bigger than that of PNIPA hydrogels in the aqueous solution of anionic surfactant sodium dodecylbenzenesulfonate(SDBS) and cationic surfactant cetyltrimethylammonium bromide(CTAB). The temperature sensitivity is improved on adding SDBS in aqueous solution. The swelling behavior of hydrophobically modified hydrogels depends on chemical structure of hydrogels and composition of solution. The swelling ratio of hydrophobically modified PNIPA hydrogels is decreased in the aqueous solution of electrolyte when acrylate hydrocarbon chain increases. The LCST value of hydrogels in the aqueous solution of SDBS is higher than that in the aqueous solution of CTAB. The range of phase transition temperature of hydrogels in the aqueous solution of SDBS is broader than that in the aqueous solution of CTAB. The temperature sensitivity, salt sensitivity, alcohol sensitivity and original swelling velocity of hydrophobically modified hydrogels is better than those of PNIPA. The LCST value of hydrogels is decreased with increasing salt concentration.The compatibility between PAA and P(NIPA-co-EA) is excellent because of the special hydrogen bond action in the network of IPN hydrogel. The Tg value of IPN hydrogels doesn't decrease linearly with PAA content increased. The LCST value of IPN hydrogels is nearly identical to that of hydrophobically modified PNIPA hydels. The IPN with proper structure hydrogels are of pH sensitivity and can che!ate heavy metal ion when medium temperature is lower than LCST value.