The production of phosphazene polymers represented by the general formula
wherein R and R' are organic radicals hereinafter defined, and wherein n is an integer from 20 upwards of 50,000 wherein one or more kinds of OR or OR' groups is attached to the phosphorus atoms in a substantially linear chain of atternat- ing P and N atoms, the groups when more than one group is present being randomly distributed along the PN backbone, as described in copending United States Patent Application Serial No. 824,004 filed August 12, 1977, is enhanced by an improved procedure forthe separation of the sodium chloride by-product from the derivatized phosphazene polymer. By treating the reaction mixture with carbon dioxide, in the presence of water and preferably with an additional alkali metal salt, agglomeration of the sodium chloride is accomplished, and a clean separation of the NaC1 from the polyphosphazene ester is more readily achieved.