A Fundamental Study on Gelation of Polymer Solutions

在溶液中将化学或物理的交联物引入线性聚合物，通常会使整个溶液凝胶。有关这一现象的基本问题包括与凝胶化机制有关的问题，以及要引入具有特定特性的聚合物溶液的临界交联数。本项目研究了三种类型的体系：(I)二羟丙基纤维素(DHPC)/硼砂/水溶液，(Ii)酰化纤维二糖(ACB)/正构烷烃溶液，(Iii)带有侧基的聚甲基丙烯酸甲酯(A-PMMA)/四氢呋喃溶液。对体系(I)和(Ii)的光谱研究表明，这些溶液的凝胶机理是清晰的。例如，在体系(I)中，凝胶是由悬挂的二醇中心和一个硼酸根离子以2：1的络合方式进行的，并且这些交联点的数目可以用^&lt；11&gt；B-核磁共振准确地确定，这表明该体系的溶胶凝胶图可以根据重叠浓度c^*缩进一条主曲线，每条链的临界交联数是c的递减函数，当c足够大时，经典的凝胶理论近似成立。体系(II)是由苯基的光二聚反应形成的化学凝胶体系。这种二聚体的数量也可以通过紫外光谱准确地确定，这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。体系(II)已被发现是一种新型的凝胶体系，其中ACB分子缔合成线性链，这些链局部凝聚成作为交联剂的液晶。

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.