Polydichlorophosphazene [NPCI2](n) reacts with the diphenol 2,2-(HO)C6H4-C6H4(OH) in THF in the presence of K2CO3 to give the polymers [NP(O2C12H8) . x(OC4H8)](n) (1) that contain variable ammouts of polytetrahydrofuran (PTHF) with x ranging from 0.05 to 0.8. This PTHF content (x) depends on the method followed to prepare the THF solutions of [NPCl2](n) used for the reactions with the biphenol and can be made negligibly small, forming these solutions in the presence of K2CO3. This reveals the presence in the [NPCl2](n) of acidic species capable of catalyzing the ring opening polymerization of THF. Polyphosphazene [NP(O2C12H8)](n) (2) was prepared completely free of PTHF using dioxane as solvent. A comparison of the thermal behavior and morphological data of the polymers 1, 2, PTHF (5), and mixtures of [NP(O2C12H8)](n) + x(OC4H8)(m) (4) revealed that the products 1 are strongly intecracting polymer blends and ruled out the possibility of block copolymers.