A novel process of manufacturing sevelamer carbonate from a polyallylamine carbonate or bicarbonate chloride salt. Process for manufacture of carbonate and/or bicarbonate salts of water insoluble polymers containing amino groups that are useful as anion binders in the gastrointestinal (GI) system. The process arranges the polyallylamine chain in a solution in such a way that the cross-linking reaction with epichlorohydrin can be controlled at a desired reaction rate.