Hydrogels based on N-isopropylacrylamide and sodium acrylate as ionic comonomer were synthesized by free radical polymerization in water using N,N′-methylenebisacrylamide as crosslinker and ammonium persulfate as initiator. The glass transition of dried copolymers poly(N-isopropylacrylamide) (PNIPA) and poly(sodium acrylate) (SA) gels and demixing/mixing transition of PNIPA-SA hydrogels swollen with increasing amounts of water were studied using conventional differential scanning calorimetry. In the crosslinked polymers, the glass transition linearly increases, and the transition range becomes broader, with increasing crosslinker content. Increasing content of ionic comonomer also produces an increase of glass transition temperature, which moves to higher temperatures with higher sodium acrylate fraction. The influence of chemical structure of PNIPA-SA hydrogels on the lower critical solution temperature (LCST) of PNIPA-SA/water mixtures during heating and cooling was quantified as function of the content of the crosslinker and the ionic comonomer, as well as water content of the hydrogel in the range from 95 to 70 wt%. At parity of water content, the LCST occurs at higher temperatures for gels containing higher amounts of sodium acrylate. Similarly, the introduction of N,N′-methylenebisacrylamide causes an increase of the LCST, which grows with increasing of crosslinking degree of the hydrogel.

中文翻译：

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交联剂和离子共聚单体浓度对共聚物聚（N-异丙基丙烯酰胺）和聚（丙烯酸钠）水凝胶的玻璃化转变和分层/混合转变的影响

以N-异丙基丙烯酰胺和丙烯酸钠为离子共聚单体，以N,N'-亚甲基双丙烯酰胺为交联剂，过硫酸铵为引发剂，在水中通过自由基聚合合成了水凝胶。使用传统的差示扫描量热法研究了干燥的共聚物聚（N-异丙基丙烯酰胺）（PNIPA）和聚（丙烯酸钠）（SA）凝胶的玻璃化转变以及随着水量增加而膨胀的 PNIPA-SA 水凝胶的分层/混合转变。在交联聚合物中，随着交联剂含量的增加，玻璃化转变线性增加，转变范围变宽。离子共聚单体含量的增加也会导致玻璃化转变温度的增加，随着丙烯酸钠含量的增加，玻璃化转变温度会上升到更高的温度。PNIPA-SA 水凝胶的化学结构对加热和冷却过程中 PNIPA-SA/水混合物的下临界溶解温度 (LCST) 的影响被量化为交联剂和离子共聚单体含量以及水含量的函数水凝胶的重量百分比为 95 至 70%。在水含量相同的情况下，对于丙烯酸钠含量较高的凝胶，LCST 在较高温度下发生。类似地，N,N'-亚甲基双丙烯酰胺的引入导致 LCST 增加，LCST 随着水凝胶交联度的增加而增加。以及水凝胶的水含量在 95 至 70 重量％的范围内。在水含量相同的情况下，对于丙烯酸钠含量较高的凝胶，LCST 在较高温度下发生。类似地，N,N'-亚甲基双丙烯酰胺的引入导致 LCST 增加，LCST 随着水凝胶交联度的增加而增加。以及水凝胶的水含量在 95 至 70 重量％的范围内。在水含量相同的情况下，对于丙烯酸钠含量较高的凝胶，LCST 在较高温度下发生。类似地，N,N'-亚甲基双丙烯酰胺的引入导致 LCST 增加，LCST 随着水凝胶交联度的增加而增加。