Synthesis and characterization of different chain length sodium polyphosphates

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 ^Dp̄ from 50 up to 25,000, that is summarized in this manuscript. NaPP with ^Dp̄ lower than 500 was obtained from fractionation of a NaPP glass. NaPP with ^Dp̄ 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 ^Dp̄ 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 ^Dp̄ 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.