Aqueous free-radical polymerization using redox system initiator that avoids adverse effects of polymerization inhibiting cations

Claim 1

In a process for preparing a water-soluble polymer from an ethylenically unsaturated monomer by free-radical polymerization in an aqueous polymerization medium in the presence of a redox system comprising an oxidizing agent and a chelatable metal reducing agent having a reduced and oxidized form and also in the presence of an impurity chelatable cation species inhibiting said polymerization, the improvements which comprise (1) adding to said polymerization medium a chelating agent which complexes said impurity chelatable cation species at a rate faster than the reduced form of said chelatable reducing agent, the amount of said chelating agent added being effective in overcoming inhibiting effects of said impurity chelatable cation species, and (2) also adding to said polymerization medium a chelatable cation species inert to said polymerization, said inert chelatable cation species being complexed at a rate slower than said impurity chelatable cation species but at a rate equal to or faster than said reduced form of said chelatable metal reducing agent, the amount of said inert chelatable cation species being in excess of the total complexing capacity of said chelating agent.