Polyacrylamide gels formed with Cr+3 ion and Cr(acetate)3: Thermodynamically and kinetically controlled crosslinking reactions

Abstract

AbstractThe gelation of buffered aqueous Cr+3/polyacrylamide (PAAm) solutions has been studied over the pH range 2‐11. With Cr+3 supplied as Cr(NO3)3 and a 7.5% hydrolyzed PAAm the upper limit for gelation was about pH 7, but Cr(acetate)3/PAAm solutions gelled as high as pH 9. Evidence is presented that the formation of unreactive colloidal Cr(OH)3(H2O)3, rather than polymer crosslinking, is favored thermodynamically for Cr+3/PAAm solutions at pH > 7. The crosslinks formed in Cr(acetate)3/PAAm solutions at pH 7–9 are deduced to be kinetically controlled products. Independent evidence for the kinetic stability of Cr+3/PAAm gels above pH 7 has also been obtained. Other observations relevant to the mechanism of crosslinking of PAAm with Cr(acetate)3 are described.