MOLEC PROCESSES IN CROSSLINKED POLYMER HYDROGEL VOLUMETRIC EXPANSION CONTRACTION

我们已经发现， 1)聚（N-异丙基丙烯酰胺），2）聚（N-正丙基丙烯酰胺），3） 聚（N-异丙基甲基丙烯酰胺）和4）聚（N-正丙基甲基丙烯酰胺） 分别在33.7、23.0、41.0和27.5 ℃下发生。 为 简而言之，将这些温度称为“转变温度”。 上述聚合物网络的质子NMR低于过渡态 温度表现出良好的分辨率光谱对应于所有 化学基团（条件A）。 就在各自的过渡上方 温度升高时，这些峰开始随着温度的升高而变宽 （条件B）并最终合并成一个宽峰（条件Q 在更高的温度范围内（比相应的温度高10至20 ° C）， 转变温度）。 这些宽峰的强度逐渐 随着温度的降低而降低。 与此同时， 所有化学基团对应的峰逐渐出现 （条件D）。 这一趋势持续了近10' C， 转变温度 这些热过程代表了 构成每个系统唯一的循环回路。 组成 2可逆（条件A至B和条件C至D）和2 不可逆（B到C和D到A）过程。 凝胶状态 在条件A和C下对应的是双稳态的 状态和条件B和D下的状态似乎是某种 具有相当长的寿命的亚稳态。 上述发现 揭示了聚合物组分在体积中的行为 收缩-膨胀的凝胶与不同的温度在 分子水平。 除了聚合物成分，质子 凝胶中HOD分子的自旋-晶格弛豫时间（T_1）也 在上述热循环中确定。 T，显著改变， 变化的温度，特别是在转变温度附近。 这种行为与密度的变化是相容的， 凝胶中的聚合物和水。 在对应于 条件C和D，HOD的T由两个分量组成， 频率间隔小。 其中一个组件可以识别为HOD 与聚合物强耦合。 通过使用密度数据，我们 可以进行T的温度依赖性的理论分析， 因此可以表征HOD分子在 凝胶。

We have found that sudden volumetric contractions of hydrogels of 1) poly(N-isopropylacrylan-~ide), 2) poly (N-n-propylacrylamide), 3) poly(N-isopropylmethacrylamide) and 4) poly(N-n-propylmethacrylamide) have occured at 33.7, 23.0, 41.0, and 27.5' C, respectively. For brevity, let these temperatures be called "transition temperatures". Proton NMR of the above polymer networks below the transition temperatures exhibited well-resolved spectra corresponding to all chemical groups (condition A). Just above the respective transition temperatures, these peaks began to broaden with increasing temperature (condition B) and eventually coalesced to one broad peak (condition Q in higher temperature ranges (10 to 20' C above the respective transition temperatures). Intensity of these broad peaks gradually decreased with lowering temperature. At the same time, broadened peaks corresponding to all chemical groups gradually appeared (condition D). This trend continued nearly 10' C beyond the transition temperatures. These thermal processes represented constitute a cyclic loop that is unique to each system. It consists of 2 reversible (conditions A to B and conditions C to D) and 2 irreversible (B to C and D to A) processes. The gel states corresponding at conditions A and C are thermodynamically stable states and those under conditions B and D seem to be some sort of meta-stable states with rather long life-time. The above finding reveals how the polymer component behaves in the volumetric contraction-expansion of gels with varying temperature at the molecular level. In addition to the polymer component, proton spin-lattice relaxation times (T,) of HOD molecule in gels were also determined in the above thermo-cycling. T, significantly changed with varying temperature, around the transition temperature, in particular. This behavior is compatible with changes in the density of both'polymer and water in gels. In the state corresponding to conditions C and D, the T, of HOD consists of two components with a small frequency separation. One component can be identified as HOD strongly coupled to the polymer. By using the data for density, we can carry out the theoretical analysis of temperature dependence of T, of HOD and thus can characterize dynamics of HOD molecules within gels.