Calorimetric Study of Order-Disorder Transition of Block Copolymers

以苯乙烯-异戊二烯两嵌段共聚物(SI)为代表的嵌段共聚物表现出规则晶格结构的微相分离。随着温度的升高，它们从有序相结构转变为无序状态。在有序-无序转变温度(ODT)附近，链的动力学和物理性质发生了很大的变化。本研究旨在阐明热力学性质与链动力学之间的关系。首先，我们构建了一台绝热量热计，用于准确测量嵌段共聚物的热容。温度计采用牛津仪器公司校准的电阻温度计(RD-Fe)，用ASL公司制造的电桥测量电阻，从而测量了电能E供应前后的温度，精度为0.0001K。样品盒由绝热墙双重包围，壁温调节到与样品盒相同的温度，误差在0.01K以内，电池镀金以防止辐射。仪表读数和温度控制由两台计算机完成。测定了SI(20wt%)在甲苯溶液中的热容。采用阴离子聚合法制备了总相对分子质量为142000，苯乙烯含量为35.9%的SI。在228K附近发现了小的光谱型异常，可归因于ODT，并与Leibler理论进行了比较。虽然热容与温度的关系与理论相符，但强度比理论高出十倍左右。除了量热研究外，我们还研究了SiI半稀溶液的介电松弛和小角X射线散射。结果发现，异戊二烯嵌段链的简正模过程的介电松弛时间在有序状态下是双峰的，但在ODT以上变为单峰。

Block copolymers such as stirene-isoprene diblock copolymers (SI) exhibit the microphase separation with a regular crystalline lattice structure. With increasing temperature, they transform from the ordered phase structure to a disordered state. Around the order-disorder transition temperature (ODT), the dynamics of the chains and the physical properties change dramatically. This study aims to clarify the relationship between the thermodynamic properties and the chain dynamics. Firstly we constructed an adiabatic calorimeter for the accurate measurements of heat capacity of block copolymers. For thermometer, a resistance thermometer (Rd-Fe) calibrated at Oxford instrument Co.was used and the resistance was measured with a bridge made by ASL Co. Thus we measured temperatures before and after the supply of electric energy E at a precision of 0.0001K.The sample cell was doubly surrounded by adiabatic walls and the temperature of the wall was regulated to be the same as the sample cell within the error of 0.01K.The cell was gold-plated to prevent the radiation. The readings of the meters and the temperature control were performed with two computers. The heat capacity of toluene solution of SI (20wt%) was measured. The SI with total molecular weight of 142000 and the stirene content of 35.9% was prepared by anionic polymerization. Small lambda type anomaly is found around 228K and can be ascribed to the ODT.The extra heat capacity due to the ODT is compared with the Leibler theory. Although the temperature dependence of the heat capacity agrees with the theory, the intensity was ca.ten times higher than the theory. Beside the calorimetric study, we investigated the dielectric relaxation and small angle X-ray scattering for semi dilute solutions of SI.It was found that the dielectric relaxation time for the normal mode process of the isoprene block chain is bimodal in the ordered state but it changes into unimodal above the ODT.