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至较高温度T_2，研究了聚合诱导的单体/聚合物混合物相分离的热历史依赖性。温度变化后畴的形态结构强烈依赖于初始相分离温度t_1的持续时间，当持续时间大于一定值时，畴的形态从液滴转变为连续畴。散射光强度的时间演化也存在热历史依赖性：在第二次跃迁后，短t_1的散射光峰值强度I_m接近于单步跃迁至T_2时I_m与时间t的曲线，而长t_1的散射光峰值强度I_m迅速超出单步跃迁至T_2时的曲线。温度变化后发生形态变化所需的最短持续时间t_1强烈依赖于初始相分离温度t_1，而与第二次相分离温度T_2无关。结果表明：在较低温度下，体系迁移率较低，聚合反应快于相分离反应；在较高温度下，体系迁移率较高，相分离反应快于反应。也就是说，T_2时的形态变化是由T_1时海相聚合产物的积累引起的。人们发现聚合诱导相分离具有很大的热历史依赖性，而热历史依赖性的研究为聚合诱导相分离提供了有价值的信息，并被证明是阐明这一现象机制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.