The condensation polymerisation of Cl₃PNSiMe₃ at room temperature is one of the best methods for polydichlorophosphazene production. The living cationic nature of the polymerisation mechanism of this material enables unique features such as the preparation of well-defined block and star polymers or organic–inorganic hybrid copolymers. Therefore, a reproducible high yield synthesis of Cl₃PNSiMe₃ from readily available and cheap chemicals under mild conditions is an important issue to be solved. In this study, PCl₅ was reacted with hexamethyldisilazane at 0 °C in various solvents to investigate the formation efficiency of Cl₃PNSiMe₃. ¹H and ³¹P NMR spectroscopic techniques were used to monitor the reaction progress and detect the available intermediates in the reaction mixture. Nonpolar solvents such as n-pentane highly decreased the formation of the side products such as Cl₃PNH and cyclic phosphazene derivatives. Thus, the isolated yield of Cl₃PNSiMe₃ was increased up to 75%. The purity of Cl₃PNSiMe₃ was over 97%, which was confirmed using ¹H, ³¹P, ¹³C and ²⁹Si NMR spectroscopic techniques. Moreover, the reaction carried out in toluene led to the direct fabrication of polydichlorophosphazene in one-pot from PCl₅ and hexamethyldisilazane in high yield (∼94%) and without the isolation of any phosphazene intermediate.