| The work in this thesis covers the synthesis of polyphosphazenes through living cationic polymerization. This new route to polyphosphazenes allows for narrow, controlled molecular weight polymers at ambient temperature. The living nature of the system also allows for control of the polymer architecture.A new method for the synthesis of poly(dichlorophosphazene) at ambient temperatures is described. It involves the initiation of Cl3P=NSiMe 3 with trace amounts of PCl5 in CH2Cl2 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.An improved synthesis of the phosphazene polymerization precursors, hexachlorocyclotriphosphazene, (NPCl2)3, (1) and Cl3P=NSiMe 3 (2), is reported. The addition of PCl5 to N(SiMe3)3 in methylene chloride at 40°C produced a mixture of phosphazenes which contained 76% of 1. However, the addition of N(SiMe3)3 to PCl5 in methylene chloride at 0°C, followed by the addition of hexane, provided 2 in 40% yield. The mechanism of the reaction is discussed.A method for the synthesis of well-defined mono-, di-, and mixed-telechelic polyphosphazenes produced via phosphoranimines and a "living" cationic polymerization is described. Molecular weights of the polymers were controlled by variation of the monomer to initiator ratios producing materials with low polydispersities.The effects of solvent, temperature, and concentration on the cationic condensation polymerization of the halophosphoranimines, Cl3P=NSiMe 3 and PhCl2P=NSiMe3 are investigated. These phosphoranimines polymerized well in dioxane, benzene, and toluene. In these solvents, the ambient temperature polymerization of PhCl2P=NSiMe3 was faster than analogous polymerizations in CH2Cl2 or CHCl3. The polymerizations Of Cl3P=NSiMe3 and PhCl2P=NSiMe3 were monitored by both NMR ( 31P and 1H) and GPC, and the kinetics of polymerization followed pseudo-first order propagation rates after a 15 to 30 minute induction period. The polyphosphazenes synthesized in toluene, benzene, or dioxane, possessed controlled molecular weights in the range of 105 with narrow polydispersities (<1.3). |
