State Key Laboratory of Molecular Engineering of Polymers, Department of Macromolecular Science and Laboratory for Advanced Materials, Fudan University , Shanghai 200433, China.
Langmuir. 2017 Oct 31;33(43):12326-12335. doi: 10.1021/acs.langmuir.7b02884. Epub 2017 Oct 16.
The microdynamic volume phase transition mechanism of poly[di(ethylene glycol)ethyl ether acrylate] (PDEGA)-based microgels with newly developed thermoresponsive polyionic liquid (PIL) (poly(tetrabutylphosphonium styrenesulfonate) P[P][SS]) moieties was studied by applying temperature-variable Fourier transform infrared (FTIR) spectroscopy in combination with two-dimensional correlation spectroscopy (2Dcos) and the perturbation correlation moving window (PCMW) technique. It can be found that the content of hydrophilic PIL moieties plays a significant role in the thermally induced phase transition behavior of microgel systems; namely, the microgels containing fewer PIL moieties present a sharp transition behavior and a gel-like state (10%, w/v) in water whereas the microgels with more PIL moieties undergo a slightly broad phase transition process and a flowable solution state. Herein, the C═O···DO-PIL hydrogen bonds as the interaction between PDEGA and P[P][SS] moieties result in a complete dehydration process for the microgels with fewer PIL moieties and the dehydrated behavior of SO groups acts as the driving force during the phase transition. As for the microgels with more PIL moieties, the whole transition process is dominated by the hydrophobic interaction of C-H groups. Even though the intermolecular hydrogen bonds (C═O···DO-PIL) appear as well, the more remarkable effect of the Coulombic repulsive force of PIL restrains the water molecules from breaking away, thus causing a gradual and incomplete dehydration process during heating.
聚[二（乙二醇）乙醚丙烯酸酯]（PDEGA）基微凝胶的微观动力学体积相转变机制，其具有新开发的温敏聚离子液体（PIL）（聚（四丁基膦苯乙烯磺酸盐）P[P][SS]）部分，通过应用变温傅里叶变换红外（FTIR）光谱结合二维相关光谱（2Dcos）和微扰相关移动窗口（PCMW）技术进行了研究。可以发现，亲水性 PIL 部分的含量在微凝胶体系的热诱导相转变行为中起着重要作用；即，PIL 部分含量较少的微凝胶呈现出明显的转变行为和水凝胶状状态（10%，w/v），而 PIL 部分含量较多的微凝胶经历稍微较宽的相转变过程和流动溶液状态。在此，C═O···DO-PIL 氢键作为 PDEGA 和 P[P][SS]部分之间的相互作用导致 PIL 部分较少的微凝胶完全脱水，而 SO 基团的脱水行为作为相转变的驱动力。对于 PIL 部分较多的微凝胶，整个转变过程主要由 C-H 基团的疏水相互作用主导。尽管也出现了分子间氢键（C═O···DO-PIL），但 PIL 的库仑斥力的更显著影响限制了水分子的脱离，从而导致在加热过程中逐渐且不完全的脱水过程。
