ASPECTS OF CROSS-LINKING SULFONATED POLYACRYLAMIDES FROM RHEOLOGICAL STUDIES ON THEIR GELS

Crosslinking of sulfonated polyacrylamide by zirconium requires some a crylate sites on polymer chain, and a schematic reaction is proposed t o describe this process. Moreover, gelation kinetics is found to be fa irly proportional to polymer acrylate site content. On the other hand, decreasing sulfonation level or solvent salt concentration is shown t o result in increasing the system gelation, and an explanation of such behavior is attempted. Furthermore, we find that gelation kinetic is highly dependent on zirconium concentration in an unusual manner. So, for a given polymer sample, a maximum of zirconium concentration exist s above which gelation kinetic decreases until it vanishes. This behav ior is interpreted by existence of a background reaction where highly stable zirconium complexes are formed. This reaction indeed competes a gainst the polymer cross-linking process and zirconium concentration i ncreases. (C) 1997 John Wiley & Sons, Inc.