Dilute solution characterization of polyfluoroalkoxyphosphazenes

Results from the dilute solution characterization of polyfluoroalkoxyphosphazenes in Freon ether (E2) solutions are reported. Anomalous viscosity data suggest that polymer aggregation sometimes occurs in E2 and may be caused by the presence of relatively few anomalous polar groups on the polymer backbone. Since small amounts of acetone added to the E2 solutions inhibit aggregate formation, samples are also characterized in an E2-acetone mixed solvent. Light scattering and osmometry indicate that E2 and E2-acetone (9.09% by volume) are theta solvents for the polymers. High molecular weights (M?_w < 3 × 10⁶) and unusually broad molecular weight distributions (M?_w/M?_n < 16) are found. One polymer is fractionated by extracting solutions in 1,1,2-trichloro-1,2,2-trifluoroethane with acetone. Although the samples are highly polydisperse, intrinsic viscosities correlate with number-average molecular weights satisfying the Mark-Houwink relation with the exponent a ≈ 1/2. The z-average mean-square radius of gyration increases linearly with molecular weight so that 〈S²〉_g/M?_w ≈ 0.098. Because of the large polydispersity and unknown form of the distribution function, a quantitative interpretation of characterization results relating dilute solution parameters to polymer skeletal structure is not possible. The tentative conclusion is that the fluoroalkoxy-substituted phosphazene polymers are relatively linear and therefore that the broad distribution of molecular weights must be due to some polymerization mechanism other than branching.