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.

Key words: HYDROLYSIS, POLYACRYLAMIDE, RHEOLOGICAL PROPERTY, REACTION KINETICS, GEL, CROSSLINKING