synopsisThe molecular weight distribution of a' vinyl chloride-vinyl acetate copolymer has been studied by three methods: (a) solution fractionation; (b) osmometry and light scat>tering; (c) gel permeation chromatography. In (a), the fractions were precipitakd from a tetrahydrofuran solution by water, then characterized. The data yielded models for the intrinsic viscosity and the molecular weight distribution, in terms of the copolymer molecular weight. In (b), the unfractionated copoIymer was characterized by osmometry and light scattering, using in the latter case the two currently accepted theories for the determination of the true weight-average molecular weight. Conflicting data suggest caution in the use of these theories. In (c), the original fractions served to establish a calibration curve which yielded exceptionally low results when applied to the analysis of the unfractionated VC-VAc copolymer. Further investigations using proposed universal calibration theories bring to light serious discrepancies.
Using pulse‐input technique, axial dispersion coefficients were determined for polystyrene in tetrahydrofuran, in toluene and in a toluene/methanol mixture flowing in a long capillary tube under conditions such that the Reynolds number was less than 500. Low polydispersity polystyrene materials with nominal molecular weights ranging from 900 to 1.8 × 106 were used. For the system studied and for fixed Reynolds numbers, the coefficient, on log‐log scales, was found to be a linear function of the product of the intrinsic viscosity and the molecular weight. An empirical equation relating this coefficient to the Reynolds number and to [η]M was obtained. This equation predicted results which agreed well with experimentally determined values.
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