| abstract |
An aqueous solution of a water-soluble polymer which can be cross-linked in the presence of certain ions by adjusting the pH of the solution is disclosed. The aqueous solution contains a cross-linkable water-soluble organic polymer and at least two cross-linking agents (ions) for said polymer, each cross-linking agent (ion) being effective to cross-link the polymer at a different pH value. The pH of the initial solution is adjusted to a value between the two effective pH values where minimal (if any) cross-linking occurs. The pH can be adjusted up or down to within a range which is effective to cross-link the polymer. |