An improved process is provided for producing polymeric acetal carboxylate salts useful as detergent builders. The process comprises polymerization of an alkyl glyoxylate, optionally with one or more comonomers; addition of stabilizing endgroups; and saponification of the polymeric ester to produce the polymeric acetal carboxylate salts. Active yield is improved by reducing the number of polymer chains with unstable temporary endcaps entering the saponification step.