A process for the preparation of polyphosphazenes is provided that includes the cationic solution polymerization reaction of a phosphoranimine, using a main group or transition metal halide, or other appropriate halide salt, including a linear phosphazene salt of any chain length, or a preformed non-phosphazene polymer containing a main or transition metal chloride, as an initiator. In a preferred embodiment, triarmed-star polyphosphazenes having the formula N{RN(H)R'.sub.2 P--(N.dbd.PR'.sub.2).sub.n }.sub.3 are prepared via this method. Also, a methods for synthesis of the monomer Cl.sub.3 P.dbd.NSiMe.sub.3 and cyclic trimer N.sub.3 P.sub.3 X.sub.6 from the reactants N(SiR.sub.3).sub.3 and PX.sub.5 are also described.