The copolymerization of styrene and acrylonitrile in bulk at 60 °C has been investigated by measurement of the copolymer/comonomer composition relationship and of the monomer sequence distributions using 13C NMR. Alternative models for the mechanism of the copolymerization have been evaluated in the most general forms, with allowance for nonzero conversions, by deriving reactivity ratios from composition data and then comparing predicted and experimental sequence distributions. The system shows significant deviations from the terminal model. Compositions cannot differentiate between penultimate and complex participation models, both of which give significant improvement over the terminal model. The measured sequence distributions are quite close to the predictions of the penultimate model but substantially different from those of the complex participation model, showing clearly that the penultimate model is the most appropriate of the models considered. We have obtained rss = 0.22g, rM = 0.03g, r^= 0.634, and rSA = 0.09v No significant improvement was observed with the antepenultimate model.

The mechanism of copolymerization of styrene and maleic anhydride in bulk at 60 "C has been investigated by measurements of copolymer compositions using 13C NMR and of monomer sequence distributions using DEPT pulse programs to distinguish CH2 subspectra, which have been attributed to styrene-centered triads. The strong tendency to alternation observed by most previous workers was confirmed. Nonlinear, least-squares analysis of the compositions of copolymers prepared over a wide comonomer composition range showed that the penultimate model gave a better fit to the data than the terminal model with a confidence level >95%. There was only a penultimate effect for styrene-terminated chain radicals. A similar analysis of the composition data of Bamford and Barb for comonomer mixtures with high styrene contents gave reactivity ratios in good agreement with the values derived from our composition data. The complex-participation and complex-dissociation models could also be fitted to the composition data but there was a strong correlation between different reactivity ratios, indicating extensive minima on the hypersurface. The monomer sequence distributions were in good agreement with the predictions of both the penultimate and complex-participation models and could not distinguish between them.ABSTRACT: The validity of terminal-model kinetics of free-radical copolymerization was critically tested against a complete set of experiments carefully carried out on the bulk copolymerization of styrene and methyl methacrylate at 40 OC. The experiments involved determining the copolymer composition, the initiation rate, the polymerization rate, the volume contraction factor, and the radical lifetime, and thus the rate constants of propagation and termination were individually evaluated as a function of monomer composition. In the rotating-sector experiments, a new system was introduced which automatically measures the migration rate of the dilatometer meniscus with high precision. The following results were obtained. The copolymer compition conforms to the terminal model (MayeLewis equation) within experimental error, whereas the propagation rate constant is entirely different from what the model predicts. As far as numerical values are concerned, the experimental data are well represented by the penultimate model. AB to the termination step, the previous results indicating large, composition-dependent values of the Walling cross-termination factor 4 are erroneous, since the validity of the terminal model is assumed in those analyses. The observed values of the termination rate constant are well represented by the chemical model with q! = 1 as well as by the North diffusion model.

a) Masuhara, H.; Ohwada, S.; Mataga, N.; Itaya, A.; Okamoto, K.; Kusabayashi, S. Chem. Phys. Lett. 1978,59,188. (b) Masuhara, H.; Ohwada, s.; Mataga, N.; Itaya, A.; Okamoto, K.; Kusabayashi, S. Kobunshi Ronbunshu 1980,37, 275. (4) Tsuchida, A.; Yamamoto, M.; Nishijima, Y. J. Polym. Sci., Polym. Chem. Ed. 1985,23, 585. (5) (a) Iwai, K.; Furue, M.; Nozakura, S.; Shirota, Y.; Mikawa, H. Polym. J. (Tokyo) 1980,12,97. (b) Iwai, K.; Itoh, Y.; Furue, M.; Nozakura, S. J. Polym. Sci., Polym. Chem. Ed. 1983,21, 2439. (6) Tazuke, S.; Yuan, H. L.; Iwaya, Y.; Sato, K. Macromolecules 1981, 14, 267. (7) This value was estimated from the oxidation potential measured by cyclic voltammetry (oxidation potential: El,* = 0.82 V vs. Ag /Ag+ for ECZ, 0.41 V vs. Ag /Ag+ for N,N-dimethylaniline, and 0.08 V vs. Ag/Ag+ for N,N,N',N'-tetramethylbenzidine) on the basis of the result obtained by: Washio, M.; Tagawa, S.; Tabata, Y. Polym. ABSTRACT The first results are reported for the quantitative application of ESR spectroscopy to emulsion polymerization kinetics. When this technique, in conjunction with dilatometric rate measurements, was applied to the seeded emulsion polymerization of methyl methacrylate a t 50 "C, the dependence of the propagation rate coefficient (k,) on the weight fraction of polymer (w,) was found to be k , = k: (0.33 5 wp 5 0.84) and k, = k: exp(-29.8[wP -0.841) (0.84 I wp I 0.99), where kPo = 790 i 300 dm3 mol-' s-l. These results reflect the passage of the latex particles through their glass transition point (at cup = OM), leading to the propagation step being controlled by the diffusion of monomer to the propagation site. The observed decrease in k , for wp > 0.84 appears to be less dramatic than that predicted by current free volume theories.ABSTRACT The character of one-dimensional order in a smectic polymer with mesogenic side groups and long spacers was studied by means of SAXS experiments, polarized microscopy, and electron microscopy over a wide temperature range, including the clearing temperature. It was demonstrated that the electron density distribution along the normal-to-smectic plane is a complicated function, characteristic of three-component systems. Such state is due to microphase separation of different fragments of macromolecules. The damping of correlation in smectic layer arrangements has an exponential form with correlation lengths of 460-600 A.The temperature increase leads to decreasing layer-packing perfection and thermal expansion of interlayer and intralayer packing. In the isotropic state a weak fluctuation of electron density, which was associated with the correlation hole effect, was observed.

The DEPT technique for the generation of CH, CH2, and CH313C NMR subspectra has enabled the resolution and assignment of broad and overlapping aliphatic resonances in copolymers. For styreneacrylonitrile copolymers, the CH2 resonances gave dyad fractions that were in agreement with the previously established copolymer structure. For styrene-maleic anhydride copolymers, three broad resonances were observed in the methylene subspectrum. These resonances were assigned to SSS, SSM and MSS, and MSM triads in preference to SS, trans-MS, and cis-MS dyads on the basis of a variety of evidence. This sequence information can be applied to the study of the mechanism of copolymerization. Partial esterification of the anhydride unit in some styrene-maleic anhydride copolymers was detected by generating the CH3 subspectrum. A modification of the DEPT sequence to obtain partially relaxed subspectra enabled and T2 relaxation times of both 13C and 1H nuclei to be measured for each of the resolved resonances.'K: 13C:-^(±x,±y)-ir(±x,±y)-acquire may be used to obtain CH" (n = 1, 2, and 3) subspectra by combination of the three spectra obtained with = /4, x/2, and 3 /4. Hence the editing depends on a pulse angle rather than a «/-modulation period as in INEPT. DEPT provides more accurate subspectra because (1) it has a lower sensitivity to V<>h variations and (2) by using fewer

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Probability theory has been used to derive equations for the complex-dissociation model for free-radical copolymerization showing how the composition, the triad fractions, and the number fractions of sequences in the copolymer are related to the comonomer composition through the reactivity ratios and the equilibrium constant for complex formation. It is shown how these equations can be used to estimate "best" values of the reactivity ratios and the equilibrium constant using experimentally determined copolymer compositions. This model has been applied to the data of Dodgson and Ebdon for the styrene-maleic anhydride copolymerization in bulk at 60 °C. The complex-dissociation model, the penultimate model, and the complex-participation model fit the copolymer/comonomer composition data equally well. However, the predicted styrene sequence distributions of the three models are quite different, and experimental determinations, for example, by 13C NMR, would enable discrimination between the models.