We report a class of stimuli-responsive poly(ionic liquid) microgel that possesses an upper critical solution temperature (UCST). Such a microgel is synthesized from ureido polymers via quaternary ammonization and post synthetic modification by anion-exchange treatment. These microgels can undergo reversible UCST-type volume phase transitions in response to the changes in temperature of water, methanol, and water/methanol mixtures, such that the temperature-responsive volume phase transition behavior can be readily tuned over a significantly wide range in a miscible mixture of water/methanol by varying the mol ratio of the two solvents, resulting in a phase diagram displaying the UCST-type co-nonsolvency phase separation phenomenon. At a set temperature in our experimental temperature window of 20.0–64.0 °C, the microgels can undergo an isothermal re-entrant swelling–shrinking–swelling transition as the methanol content increases in the water/methanol mixture. Moreover, these microgels as catalysts in a model esterification reaction of palmitic acid with methanol can display merits of both homogeneous (considerably high efficient catalytic activity) and heterogeneous (excellent recyclability) catalysis. With UCST-type responsive phase behavior and catalytic properties harnessed on the same object, the microgels react to external stimuli which allows their catalytic properties to be altered accordingly, to a certain extent, in a novel non-monotonous way different from that reported previously on the catalyst systems using LCST-type microgels.

中文翻译：

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脲基衍生的UCST型聚（离子液体）微凝胶的合成与表征†

我们报告了一类具有上临界溶液温度（UCST）的刺激响应性聚（离子液体）微凝胶。这种微凝胶是由脲基聚合物经季铵化合成的，并通过阴离子交换处理进行合成后修饰。这些微凝胶可以响应于水，甲醇和水/甲醇混合物的温度变化而经历可逆的UCST型体积相变，从而可以轻松地在很宽的范围内调节温度响应的体积相变行为。通过改变两种溶剂的摩尔比将水/甲醇混溶，得到的相图显示了UCST型共非溶解性相分离现象。在我们实验温度范围内的设定温度20.0–64.0°C下，随着水/甲醇混合物中甲醇含量的增加，微凝胶会经历等温折返膨胀-收缩-溶胀转变。此外，这些微凝胶在棕榈酸与甲醇的模型酯化反应中作为催化剂，可以显示均相（非常高效的催化活性）和非均相（出色的可回收性）催化的优点。由于UCST型响应相行为和催化特性都作用于同一物体，所以微凝胶对外部刺激起反应，从而使其催化特性在某种程度上以一种不同于先前报道的新颖，非单调的方式发生了变化。使用LCST型微凝胶的催化剂体系。