The outcome of the reaction of the bifunctional reagent p-aminophenol (HO-C6H4-NH2) with the cyclic triphosphazene [N3P3Cl6] is very dependent on the solvent, the temperature, and the proton abstractor. In THF at room temperature with K2CO3 the reaction is very slow and takes place only through the NH2 group to give a mixture of aminophosphazenes, but in refluxing acetone with Cs2CO3 the reaction is fast and occurs through both the NH2 and the OH groups leading to crosslinked products. The analogous reaction with the bis-spirocyclodichlorotriphosphazene [N3P3Cl2(O2C12H8)2] (O2C12H8 = 2,2′-dioxybiphenyl) is also dependent on the conditions, but is more selective. At room temperature in THF with K2CO3 the reaction gives mostly aminophosphazene derivatives, while in refluxing acetone with Cs2CO3 the known aryloxyphosphazene [N3P3(OC6H4NH2)2(O2C12H8)2] (1) is obtained exclusively. Accordingly, the reactions of p-aminophenol with high molecular weight poly(dichlorophosphazene) [NPCl2]n in THF at room temperature in the presence of K2CO3, occur exclusively through the NH2 groups without crosslinking, forming solutions of the aminophosphazene random copolymers {[NPCl2]1−x[NPCl(NHC6H4OH)]x}n (2a) (x 1) that carry terminal OH groups. The reaction of 2a with NH2Bu (Bu = n-butyl) gave the stable and soluble polymers {[NP(NHBu)2]1−x[NP(NHBu)(NHC6H4OH)]x}n (3). Also, in agreement with the cyclic models, the reaction of p-aminophenol with the partially substituted copolymer {[NP(O2C12H8)]0.8[NPCl2]0.2}n occurs only at refluxing temperatures and in the presence of Cs2CO3, producing the poly(aryloxyphosphazene) derivative {[NP(O2C12H8)]0.8[NP(OC6H4NH2)2]0.2}n (4) possessing terminal NH2 groups, or, if the chlorine substitution is completed with phenol, the analogous polymer {[NP(O2C12H8)]0.8[NP(OC6H5)(OC6H4NH2)]0.2}n (5). (© Wiley-VCH Verlag GmbH, 1 Weinheim, Germany, 2002)