or as water-absorbent agents.They may also be used to prepare synthetic units for synthesis in organophosphorus chemistry.The inventive and novel polymeric phosphinic acids and their salts may be described by the formula (I)##STR00008## where X is hydrogen or 1/m of a metal of valency m, or is a protonated nitrogen base, R.sub.1 and R.sub.2 may be identical or different and are hydrogen, a carbox