MOLEC PROCESSES IN CROSSLINKED POLYMER HYDROGEL VOLUMETRIC EXPANSION CONTRACTION

我们发现，水凝胶的突然体积收缩 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) 分别发生在33.7℃、23.0℃、41.0℃和27.5℃。为 简而言之，让我们把这些温度称为“转变温度”。 上述聚合物网络在相变下方的质子核磁共振 温度表现出很好的分辨光谱，对应于 化学基团(条件A)。就在各自过渡的上方 随着温度的升高，这些峰开始变宽。 (条件B)并最终合并成一个宽峰(条件Q 在较高的温度范围(高于各自的温度10至20摄氏度 转变温度)。这些宽峰的强度逐渐增大 随温度降低而降低。同时，扩大了 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摄氏度之后 转变温度。这些热过程代表了 构成每个系统唯一的循环循环。它包括 2个可逆的(条件A到B和条件C到D)和2 不可逆(B到C和D到A)过程。凝胶态 相应的条件A和C在热力学上是稳定的 国家和那些处于B和D条件下的国家似乎是某种 亚稳定态具有相当长的寿命。上述发现 显示聚合物组件在体积中的行为方式 在不同温度下凝胶的收缩-膨胀 分子水平。除了聚合物成分，质子 HOD分子在凝胶中的自旋-晶格弛豫时间(T_1) 在上面的热循环中确定。T，显著改变为 温度变化，特别是在转变温度附近。 此行为与密度的变化兼容 聚合物和水都以凝胶形式存在。在对应于的状态下 条件C和D，即HOD的T，由两个部分组成，其中 频率间隔小。其中一个组件可以标识为HOD 与聚合物强偶联。通过使用密度数据，我们 可以进行T随温度变化的理论分析， 因此可以表征体内HOD分子的动态变化 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.