Clarification of the Mechanism of Thermoreversible Sal-Gel Transition of Non-crystalline Polymer/Diluents

本文通过对无规聚苯乙烯(APS)/二硫化碳(CS_2)体系的中子散射、落球法、差示扫描量热法(DSC)和特性粘数的测定，揭示了溶胶-凝胶转变的机理。即使在溶胶中，前凝胶也是由APS链之间的链间缔合形成的。通过对APS链在无限稀释和高相对分子质量范围内的粘度分析，认为APS链是由强的链间缔合作用形成的一种球状螺旋。随着浓度的增加，溶胶-凝胶转变曲线上的临界散射指数从3.3变化到2.0。结果表明，交联区具有柔软的结构，即其行为类似于流体结核。广角中子散射的结果表明，凝胶的结构在很大程度上取决于凝胶的制备温度。软交联区源于溶剂分子参与交联物的形成。综上所述，目前的物理凝胶可能是具有软交联的相分离凝胶。

In the present work, the results of the neutron scattering, the ball-drop method, DSC, and the intrinsic viscosity on atactic polystyrene (aPS)/carbon disulfide (CS_2) system were presented to reveal the mechanism of the sol-gel transition. The pregel is formed by the interchain association among aPS chains even in the sol. Through the analysis of the viscosity in the limits of both infinite dilution and high molecular weight, the aPS chain behaves as a kind of globular coil, which is induced by the strong interchain association. The critical scattering exponents along the sol-gel transition curve change from 3.3 to 2.0, as the concentration increases. The result suggests that the cross-linking region has a soft structure, i.e., it behaves like a fluid nodule. The results on the wide-angle neutron scattering suggest that the gel structure largely depends on the preparation temperature of the gel. The soft crosslinking region originates from the participation of the solvent molecule in the formation of the crosslinks. As a conclusion, present physical gel may be the phase separating gel with soft corsslinks.