Novel poly(ethylene glycol)/poly(2‐acrylamido‐ 2‐methylpropanesulfonic acid‐co‐N‐isopropylacrylamide) semi‐interpenetrating network gels were synthesized with free‐radical initiation at 70°C and characterized with differential scanning calorimetry, Fourier transform infrared and X‐ray photoelectron spectroscopy, X‐ray diffraction, and scanning electron microscopy. The first thermal decomposition peaks for semi‐interpenetrating network gels with various proportions of 2‐acrylamido‐2‐methylpropanesulfonic acid and N‐isopropylacrylamide were in the range of 278–289°C, whereas for poly (2‐acrylamido‐2‐methylpropanesulfonic acid‐co‐N‐isopropylacrylamide) copolymer gels with corresponding proportions of the comonomers, decomposition began at about 203°C. A significant proportion of the amide groups in the semi‐interpenetrating network gels with a high proportion of 2‐acrylamido‐2‐methylpropanesulfonic acid were found to be protonated as a result of the relatively strong acid strength of 2‐acrylamido‐2‐methylpropanesulfonic acid. The surface morphology of the dried gels varied with the relative proportions of the comonomers and was significantly different for the semi‐interpenetrating network gels and corresponding copolymer gels. Strong hydrophobic and hydrogen‐bonding interactions between poly (ethylene glycol) with an average molecular weight of approximately 6000 g/mol and the copolymer network were responsible for different thermal behaviors of the poly(2‐acrylamido‐2‐methylpropanesulfonic acid‐co‐N‐isopropylacrylamide) copolymer gels and the semi‐interpenetrating network gels.
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Zhang et al. (2007) studied this question.
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