A new method for the synthesis of poly(dichlorophosphazene) at ambient temperatures is described. It involves the initiation of Cl3P=NSiMe(3) with small amounts of PCl5 in CH(2)CL(2) to yield poly(dichlorophosphazene), (NPCl2)(n), with narrow polydispersities. The molecular weight of poly(dichlorophosphazene) was controlled by altering the ratio of monomer to initiator. The polymer chains were found to be active after chain propagation since further addition of monomer resulted in the formation of higher molecular weight polymer. Integration of H-1 and P-31 NMR spectra of these reactions revealed that the polymerization follows first-order reaction kinetics with respect to monomer concentration Active polymer chains may be quenched or end-capped by the addition of trace quantities of Me(2)(CF3-CH2O)P=NSiMe(3) or (CF3CH2O)(3)P=NSiMe(3). Furthermore, PBr5, SbCl5, and Ph(3)C[PF6] were also found to be effective initiators in CH2Cl2 at room temperature.