Abstract: Molecular dynamics simulation at all atoms level was used to probe the temperature induced phase transition behavior of single-chain block copolymer PEO-PPO-PEO, represented by Pluronic P85, in different solutions. A negative temperature responsiveness of Pluronic P85 in polar solvent such as water and methanol was observed, in which the increase in temperature promoted the breakage of hydrogen bonds between the PPO and PEO respectively with the solvents and thus resulted in the desolvation of PPO and PEO. This thus led to collapse of the polymer as a result of enhanced intramolecular interaction and the release of solvent molecules. On the contrary, a positive temperature responsiveness of Pluronic P85 was shown in toluene, in which the increase in temperature weakened the intramolecular interaction and thus enabled conformational flexibilities. The temperature responsiveness of the solvation of PEO and PPO block was also simulated, which offered a theoretical basis for the molecular design and applications of these PEO-PPO-PEO block copolymers.

Key words: PEO-PPO-PEO, organic solvents, molecular dynamics simulation, phase behavior

摘要： 以Pluronic P85为例，采用全原子分子动力学模拟方法研究了单链嵌段类共聚物PEO-PPO-PEO在不同溶剂中的温敏性相转变行为及其影响机制。分子模拟结果显示当Pluronic P85溶解在水溶液和极性有机溶剂（甲醇）中时，升温导致PPO和PEO与水或甲醇分子间氢键断裂、使得溶剂化壳层被破坏而释放出水或甲醇分子，Pluronic P85发生构象塌缩，呈现反向温度响应特性。当Pluronic P85溶解在非极性有机溶剂（甲苯）中时，升温导致分子热运动加剧而削弱Pluronic P85链分子内相互作用，使其在甲苯中的构象更加舒展，呈现正向温敏特性。分子模拟结果还展现了PEO和PPO链段的溶剂化效应随温度的变化及其对于聚合物构象的影响，对于此类聚合物的分子设计和应用提供了理论依据。

关键词: PEO-PPO-PEO, 有机溶剂, 分子模拟, 相变行为