DILUTE-SOLUTION CHARACTERIZATION OF POLY(DIHEXOXYPHOSPHAZENE)

A sample of poly(dihexoxyphosphazene) (PDHP) has been synthesized, purified, characterized, and fractionated according to standard procedures. Four fractions were separated and studied by light scattering, viscometry, and size-exclusion chromatography. The light scattering measurements, performed in THF solutions at 25-degrees-C, gave MBARw = 2.3, 0.92, 0.25, and 0.026 x 10(6), respectively, for fractions 1-4; the values of the second virial coefficient decrease with increasing molecular weight, and thus A2 = 0.66, 1.27, 1.67, and 3.98 X 10(-4) mol cm3 g-1, respectively, for fractions 1-4; fraction 4 had a radius of gyration too small to be determined with accuracy; the results for the other three fractions were <s2>1/2 = 71, 30, and 16 nm. Intrinsic viscosities of the four fractions, measured in THF solutions at 25-degrees-C, were [eta] = 1.745, 1.151, 0.425, and 0.064. Two iterative numerical procedures previously described in the literature were 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; both methods give approximately the same results. The K and a constants of the Mark-Houwink equation allow the determination of the viscosity-average molecular weight of the four fractions MBARv, and their molecular dimensions, that are concordant with those measured by light scattering.