Thermal-History Dependence of Dynamics of Polymerization-Induced Phase Separation and Its Mechanisms

通过在相分离过程中逐步升温到更高的温度T2，研究了单体/聚合物混合物聚合诱导相分离的热历史依赖性。温度变化后微区的形态结构强烈依赖于初始相分离温度下的持续时间t1：当持续时间超过一定值时，微滴形态发生变化，形成连续的微区。在散射光强度的时间演化中也发现了热历史相关性：在短t_1的情况下，第二跳后，峰值强度I_m接近一步跳到T_2的I_m-时间t曲线。温度变化后发生形态变化所需的最短持续时间t1强烈依赖于初始相分离温度T_1，而与第二相分离温度T_2无关。这些结果解释为：在较低温度下，体系的迁移率较低时，聚合反应快于相分离，而在较高温度下，相分离较快，在较高温度下，迁移率较高。也就是说，T_2的形态变化是由T_1时聚合产物在海相中积累引起的，聚合诱导相分离具有很大的热历史依赖性，热历史相关性的研究提供了关于聚合诱导相分离的有价值的信息，并被证明是解释这一现象机理的一种非常有用的方法。

Thermal-history dependence of polymerization-induced phase separation of a monomer/polymer mixture was studied by making a stepwise temperature change to a higher temperature T_2 in the course of phase separation. Morphological structure of domains after the temperature change strongly depended on the duration t_1 at the initial phase-separation temperature : Morphological change from droplets to continuous domains occurred when the duration was longer than a certain value. Thermal-history dependence was found in the time evolution of scattered light intensity as well : After the second jump, the peak intensity I_m approached the curve of I_m vs. time t for the single-step jump to T_2 in the case of short t_1, while in the case of long t_1 increased rapidly beyond the curve for the single step to T_2. The shortest duration time t_1 required for occurrence of morphological change after the temperature change was strongly dependent on the initial phase-separation temperature T_1 but independent of the second temperature T_2. These results were explained as follows : Polymerization reaction was faster than phase separation at a lower temperature where mobility of the system was low, while phase separation was faster than reaction at a higher temperature where the mobility was high. In other words, the morphological change at T_2 was caused by the polymerization product accumulated in the sea phase at T_1.Polymerization-induced phase separation was found to have a large thermal-history dependence, and examination of thermal-history dependence gave valuable information about polymerization-induced phase separation and was proved to be a very useful method for elucidating the mechanisms of this phenomenon.