MOLECULAR CHARACTERIZATION OF POLY[BIS BETA-NAPHTHOXY)PHOSPHAZENE] BY P-31 NMR, VISCOMETRY, LIGHT-SCATTERING, AND SIZE EXCLUSION CHROMATOGRAPHY

A sample of poly[bis(beta-naphthoxy)phosphazene] (PBNP) has been synthesized, purified, fractionated, and characterized according to standard procedures. Seven fractions were separated and studied by light scattering, viscometry, and size exclusion chromatography(SEC). The light scattering measurements, performed in THF solutions at 25-degrees-C, gave M(w)BAR = 140, 120, 54, 50, 42, 21, and 10 in 10(4) g/mol units, respectively, for fractions 1-7; the results for the radius of gyration for the fractions were [s2]1/2 48, 40, 31, 31, 31, 25, and 16 nm, and the intrinsic viscosities measured in THF solutions at 25-degrees-C were [eta] = 0.72, 0.47, 0.38, 0.29, 0.25, 0.18, and 0.12 dL/g. An iterative numerical procedure previously described in the literature was employed to combine all the experimental results, seeking the best choice of the parameters defining both the SEC calibration curve and the Mark-Houwink equation. The results obtained for those functions were log M = 14.93 - 2.54V + 0.16V2 and [eta] = 4.17 X 10(-5) M0.69. The K and a constants of the Mark-Houwink equation allow the determination of the viscosity average molecular weight of the seven fractions, M(v)BAR and their molecular dimensions, which are smaller than those measured by light scattering. The analysis of the results obtained by light scattering and viscometry, together with the P-31 NMR spectra of the samples, allows one to reach some conclusions about the possible branching of this polymer.