The accuracy of 13C nuclear magnetic resonance (13C NMR) measurements has been examined by using 14C-labeled ethylenepropylene (EP) copolymers. The monomer compositions calculated from the methylene and methine resonances are in agreement with those determined by radioassay within a relative error of 4%. These results indicate that the NOES are uniform, at least for such carbons, and, therefore, the monomer sequence distributions obtained are sufficiently reliable. Monomer reactivity ratios, rl (ethylene) and rz (propylene), have been calculated from the dyad distribution and the monomer feed composition. The observed triad distribution, compared with that calculated by a first-order Markovian scheme using rl and r2, shows the peculiarity that ethylene tends to copolymerize either in alternation or in runs.ABSTRACT: Two samples of poly(viny1 bromide) were prepared and purified. Sample A was synthesized by radical polymerization of vinyl bromide at 35 "C, and sample B was obtained by extraction of sample A with dioxane at room temperature. Both samples had an isotactic content (determined by I3C NMR) of 46%. Molecular weight averages were calculated from viscometric measurements in THF solutions and were found to be 52 100 and 27 400 for samples A and B, respectively. Dielectric measurements were performed in solutions of both samples in dioxane and 1-methylnaphthalene at several temperatures, and dipole ratios D, = (fi2)/xm2 were found to be 0.53 and 0.45 in dioxane and 1-methylnaphthalene, respectively. No noticeable dependence of D, with molecular weight was found; the variation of D, with temperature was too small to allow an accurate determination of its temperature coefficient. A rotational isomeric state model was derived and used to calculate dipole and characteristic (C, = (P)o/nF) ratios. Theoretical values of both D, and C, are in good agreement with experimental results.

Nascent polypropylene particles prepared with S-TiCl3 catalyst systems have been examined by small-angle X-ray scattering, wide-angle X-ray diffraction, and electron microscopy. The catalyst crystallites which disperse at the initial stage of polymerization uniformly within the polymer particles retain their initial size during the course of polymerization. As the polymerization proceeds, the 0.2-0.35-jtm primary polymer particles become visible under an electron microscope, and their size increases in proportion to the cube root of the polymer yield.

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