Synthesis and characterization of different chain length sodium polyphosphates

•We describe synthesis of different chain length sodium polyphosphates.•Short chain polyphosphates were synthesized by fractionation.•Long chain polyphosphates were synthesized by an ion-exchange process.•Synthesized polyphosphates were characterized by a variety of methods.•The paper could be used as a comprehensive guide for synthesis of this polymer.

The simple chemistry of sodium polyphosphate (NaPP) makes it a very safe inorganic polymer for bio-applications. Recently we have focused on an in-situ forming system comprised of NaPP and calcium chloride solutions which, on contact, form a gel-like material. This system could be used in a variety of bio-applications. The first step of our studies has been synthesis and characterization of NaPP with the average degree of polymerization Dp¯ from 50 up to 25,000, that is summarized in this manuscript. NaPP with Dp¯ lower than 500 was obtained from fractionation of a NaPP glass. NaPP with Dp¯ higher than 500 was obtained from an ion-exchange process on a potassium polyphosphate crystalline phase. The ion-exchange process was optimized maximizing the potassium exchange with sodium while minimizing resin waste. The Dp¯ of prepared NaPPs was determined by titration, viscosity and 31P-liquid nuclear magnetic resonance measurements. The accuracy of these methods in determining the chain length is discussed. The effect of furnace time and temperature on Dp¯ is also discussed. In addition, since both fractionation and ion-exchange methods introduce water, the resulting NaPPs were evaluated for residual water by differential scanning calorimetry and elemental analysis methods.