Measurement of Pol Ymerization Degree of Condensed Phosphates by Solid-state Nmr

Measurement of polymerization degree of condensed phosphates was examined by solid-state NMR. Broad peaks of the NMR of endand middle-PO4 groups of condensed phosphates were observed at about 1 and -20 ppm, respectively. The NMR. peak area ratio (Ro) of middle-PO4 group to end-PO4 group has the following relation with the polymerization degree (n) of polyphosphate: Ro (middle-PO4/end-PO4) = (n-2)/2 Calculated polymerization degrees of polyphosphates agreed well with measured ones and it is found that the solid-state NMR technique is useful to the measurement of polymerization degree of water-insoluble solid-state condensed phosphates having a chain structure. INTRODUCTION The measurement of polymerization degree of condensed phosphates is possible for only water-soluble polyphosphates and is usually made by the pH titration method.1,2 The measurement of polymerization degree of water-insoluble condensed phosphates is difficult and an useful method has not been developed to those condensed phosphates yet. Solid-state NMR can be used for the measurement of chemical shifts of end-PO4 and middle-PO4 groups and these groups indicate peaks at around 1 and -20 ppm, respectively. The peak area of 31P NMR is proportional to the number of phosphorus. Accordingly, the peak area ratio (Ro) of middle-PO4 group to end-PO4 group has the following relation with polymerization degree (n) of polyphosphate: Received June 4, 2000; Accepted October 23, 2000