Synthesis and characterization of polyaryloxyphosphazenes

Abstract

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) 2 PN] n , with Ar = C 6 H 5 , m ‐ and p ‐CH 3 C 6 H 4 , m ‐ and p ‐ClC 6 H 4 , p ‐C 2 H 5 C 6 H 4 , or p ‐CH 3 OC 6 H 4 . 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 ( M̄ w > 6 × 10 5 ) and broad molecular weight distributions ( M̄ w / M̄ n > 4.7). The experimental values for the Z ‐average radii of gyration, 〈 S 2 〉 z 1/2 , 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.