A Fundamental Study on Gelation of Polymer Solutions

将化学或物理交联引入到溶液中的线性聚合物中，通常使整个溶液凝胶化。关于这一现象的基本问题包括与胶凝机制有关的问题，以及引入具有给定特性的聚合物溶液的交联的临界数量。本项目用三种类型的体系处理了这些问题：(I)二羟丙基纤维素(DHPC) /硼砂/水溶液，（II）酰基化纤维二糖(ACB) /正烷烃溶液，（III）带有悬垂苯基的聚甲基丙烯酸甲酯(A-PMMA) /四氢呋喃溶液。系统(I)和（II）的光谱研究，这是物理胶凝系统，明确了这些溶液的胶凝机制。例如，在系统(I)中，胶凝发生在一个2：结果表明，该体系的溶胶-凝胶图可以用重叠浓度c^*来表示为一条主曲线，每条链的临界交联数是c的递减函数，当c足够大时，经典的凝胶化理论基本成立。系统（II）是由蒽基光二聚化引起的化学胶凝系统。这种二聚体的数量也可以通过紫外光谱准确地确定，并与交联链的分子量和半径的光散射数据一起表明，经典理论在高浓度下也适用于该体系。系统（II）是一种新型的胶凝系统，其中ACB分子结合成线性链，局部凝固成液晶作为交联。

Introduction of chemical or physical crosslinks to a linear polymer in solution often gels the whole solution. Fundamental problems regarding this phenomenon include those related to the mechanisms of gelation and the critical number of crosslinks to be introduced to a polymer solution with givencharacteristics. This project has dealt with these problems with three typesof systems : (I) dihydroxypropylcellulose (DHPC) /borax/aqueous solutions, (II) acylated cellobiose (ACB) /n-alkane solutions, and (III) poly (methyl methacrylate) with pendant anthryl groups (A-PMMA) /tetrahydrofuran solutions.Spectroscopic studies on systems (I) and (II) , which are physically gelling systems, have made clear the mechanisms of gelation of those solutions. In system (I) , for example, the gelation takes place by a 2 : 1 complexation of the pendant diol sites and a borate ion, and the number of these crosslinking sites could be accurately determined by ^<11>B-NMR,showing that the sol-gel diagrams of this system can be scaled into a single master curve in terms of the overlap concentration c^*, that the critical number of crosslinks per chain is a decreasing function of c, and that the classic gelation theory approximately holds when c is sufficiently large. System (II) is a chemically gelling system induced by the photodimerization of the anthryl groups. The number of such dimers could also be accurately determined by UV spectroscopy, which along with light scattering data of the molecular weight and radius of the crosslinked chains has shown that the classic theory holds also in this system at high concentrations. System (II) has been found to be a new type of gelling system in which ACB molecules associate into linear chains, which locally coagulate into liquid crystallites working as crosslinks.