Synthesis and characterization of polyaryloxyphosphazenes

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Abstract
The synthesis, dilute solution characterization, and thermal analysis of seven polyaryloxyphosphazenes are described. Synthesis is accomplished by the ring‐opening polymerization of hexachlorocyclotriphosphazene at 245°C, followed by reaction of polydichlorophosphazene with sodium aryloxide salts in solution at 115°C. Polymers prepared and characterized have the general structure [(ArO)2PN]n, with Ar = C6H5, m‐ and p‐CH3C6H4, m‐ and p‐ClC6H4, p‐C2H5C6H4, or p‐CH3OC6H4. Elemental and infrared analyses show these polymers are essentially free of reactive chlorine sites. All the polymers displayed high intrinsic viscosities [η] > 1 dl/g, in tetrahydrofuran or chloroform. Closer examination of the dilute solution properties of two polyaryloxyphosphazenes revealed high molecular weights (M̄w> 6 × 105) and broad molecular weight distributions (M̄w/M̄n > 4.7). The experimental values for the Z‐average radii of gyration, 〈S2〉z1/2, characterized at near theta conditions, are larger than the calculated values for a freely rotating chain, which suggests that these polymers are relatively linear and not highly branched. Thermal analysis revealed second‐order glass transitions between −37 and +13°C and first‐order endothermic transitions between 43 and 160°C for the different polymers. Although crystalline structure can persist above this first‐order transition, this temperature can be regarded as a melting temperature or softening temperature at which films can be molded. Decomposition temperatures, measured in argon and oxygen, ranged from 250°C to 400°C.