聚碳酸酯物理老化的二个热流转变

Sub-T_g Heat Flow Transition of Polycarbonate

聚碳酸酯 (PC)物理老化中的二个热流转变现象的研究发现 :sub Tg 热流转变开始于较低温度 ,并随之移向高温 ,最终形成一个转变 .玻璃化转变温度随此前的降温速率而变化 ,并存在一最低点 ,只有老化前的冷却速率高于该速率时 ,样品老化后才会出现sub Tg 热流转变 .同时淬火的起始温度与这一热流转变也有着直接的联系 .这一现象与环氧树脂相似 ,sub Tg 转变可以被归结为内应力已松弛的链段的热运动 .

Two heat flow transitions of polycarbonate (PC) after physical aging have been studied. Sub T g heat flow transition appears at lower temperature and moves to higher temperature with aging time. After long aging time, two heat flow transitions merges into one. Glass temperature changes with the prior cooling rate and there exists and lowest T g. Only when the cooling rate is higher than the rate appearing the lowest T g, sub T g heat flow transition can be observed after aging and it can be ralated to the quench temperature. All these observations are similar to those of epoxy resin. Sub T g heat flow transition could be attributed to the molecular motion of internal stress relaxed chain.