Study of degradation of polyphosphates in aqueous solution

AbstractCyclic trimetaphosphate is formed along with monophosphate and some di‐ and triphosphate on the degradation of chainlike polyphosphates in aqueous solution at pH 8 and 60°C. This degradation is catalytically accelerated by many metal salts. The kinetic examination of the degradation reaction in the presence of some selected metal salts shows that its catalytic effect is closely connected with the ion exchange capacity of the polyphosphates. The higher the affinity of a metal cation to the polyphosphate, i.e., the stronger it is bound, the higher is its catalytic activity. This increases in the order K < Na < Li < Ba < Sr < Ca < Mg < Al. From the kinetics of the degradation reaction it follows, contrary to our previous investigations, that degradation does not occur only from the chain end but statistically over the whole polymer molecule and that the formation of trimetaphosphate is not connected with the formation of the monophosphate. A new scheme of reaction for the formation of the cyclic trimetaphosphate from the chainlike polyphosphates is developed. According to this the primary step of the degradation consists of an intramolecular “phosphorylation” of the polyphosphate, which is then followed by hydrolysis of the trimetaphosphate.