Research Center for Analytical Sciences, College of Chemistry, Nankai University, Tianjin 300071, P. R. China.
Phys Chem Chem Phys. 2019 Mar 6;21(10):5780-5789. doi: 10.1039/c8cp07153e.
For understanding the role of water in the aggregation of polymers, the variation of water structures with the structural change of polymers in the process of aggregation was studied by temperature-dependent near-infrared (NIR) spectroscopy. The NIR spectra of the aqueous poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) solutions of different concentrations were measured at different temperatures. The spectral changes of the polymer and water with temperature were analyzed by N-way principal component analysis (NPCA). It was found that, at low concentration, the chains of the polymer tend to form a loose hydrophobic structure below 36 °C and then aggregate into a micelle at a lower critical solution temperature (LCST) of around 39 °C. In the process of the aggregation, the water species with two hydrogen bonds (S2) increases gradually before 36 °C and then a sudden decrease occurs after that temperature. The results clearly indicate that water species S2 plays an important role in the formation of the intermediate, i.e., the loose hydrophobic structure of the polymer chains linked by the two hydrogen bonds of S2 water. When the temperature increases, the dissociation of the hydrogen bonds enables the intermediate to be destroyed to form a micelle structure. For the high concentration solution, however, the spectral information of S2 was not found in the aggregation, suggesting direct formation of the micelle from the dehydrated chains.
为了理解水在聚合物聚集过程中的作用，通过温度依赖的近红外（NIR）光谱研究了聚合物结构变化过程中水中结构的变化。在不同温度下测量了不同浓度的聚（N，N-二甲基氨基乙基甲基丙烯酸酯）（PDMAEMA）水溶液的近红外光谱。通过 N 路主成分分析（NPCA）分析了聚合物和水随温度的光谱变化。结果发现，在低浓度下，聚合物链在 36°C 以下倾向于形成松散的疏水性结构，然后在约 39°C 的低临界溶液温度（LCST）下聚集形成胶束。在聚集过程中，在 36°C 之前，具有两个氢键的水物种（S2）逐渐增加，然后在该温度之后突然减少。结果清楚地表明，水物种 S2 在中间产物的形成中起着重要作用，即由 S2 水的两个氢键连接的聚合物链的松散疏水性结构。当温度升高时，氢键的解离使中间产物被破坏，形成胶束结构。然而，对于高浓度溶液，在聚集过程中未发现 S2 的光谱信息，表明从脱水链直接形成胶束。
