流变学法研究部分水解聚丙烯酰胺/Cr(III)交联反应I.浓度的影响

采用流变学法系统地考察了部分水解聚丙烯酰胺（HPAM）/Cr(III)交联体系的 反应动力学。HPAM溶液的粘性模量G”大于弹性模量G’,且其数值随时间不发生变 化,体系为粘性溶液。而HPAM/Cr(III)体系的G’和G”的数值都随时间变化,G” 在反应开始阶段大于G’,当反应进行一段时间后,G’超过G”占据主要地位,体 系成为弹性体系。交联过程可分为三个阶段：第一上升阶段,平缓上升阶段和第二 上升阶段。利用G’～ t曲线可以推测反应机理。实验发现成胶速率随反应物HPAM 和Cr(III)的浓度的增加而增加,而成胶时间缩短。在羧基浓度过量的情况下,交 联反应对Cr(III)浓度的反应级数是1。凝胶的有效弹性交联密度随聚合物浓度的增 加而增,且随凝胶反应的进行而增加。凝胶的交联点间的平均分子量随Cr(III)浓 度的增加和交联反应的进行而下降。

Rheological Study of the Crosslinking Reaction between Polyacrylamide and Cr(III) I. Effect of Concentration

Rheological measurements have been performed on a system of HPAM with Cr(III) as a crosslinking agent. For the HPAM solution, the viscous modulus G" is higher than the elastic modulus G'. Both values do not change with time and the solution is a viscous system. For the crosslinking system, G' value increased and exceeded the G" value and the gelling solution displays more solid or elastic properties. The kinetics of the gelation was determined from measuring the time dependence of G'. The gelation process consists of three periods, i.e. The first increasing period, the slow increasing period and the second increasing period. The relative gelation rates of the HPAM/Cr(III) systems can be measured by using the initial G' versus time slopes to represent the rates of gelation. We found that the gelation rates increased with the concentrations of HPAM and Cr(III), and the G'-G" crossing time became shorter. We observed a first-order reaction for Cr(III) under the conditions that the carboxylate groups are in excess. The elastic effective crosslinking density of the gelling fluid increases with the polymer concentration and with the gelation process. The average molecular weight of the chains adjoining adjacent crosslinks decreases slightly with the crossliner concentration and with the gelation process.