Model copolymerization reactions: determination of the relative rates of addition of styrene and acrylonitrile to the benzyl radical

Abstract

Reductive demercuration of benzylmercuric chloride in CH2C12 solutions affords toluene and bibenzyl as major products in a ratio of ca. 4:3. In similar solutions that contain styrene and acrylonitrile, one obtains not only toluene and bibenzyl but also 1,3-diphenylpropane (11), 1,2,4-triphenylbutane (12), 4-phenylbutyronitrile (13), and 2-benzyl-4-phenylbutyronitrile ( 14). Each of these products can be rationalized on the basis of a reaction scheme in which addition of the benzyl radical to styrene or acrylonitrile is followed by trapping of the adduct by transfer of a hydrogen atom or a benzyl fragment. The product ratios 11:12 and 13:14 were found to be independent of reaction conditions within the range of conditions employed in this work. The relative rates of addition of styrene and acrylonitrile (ks/kA) were determined by analysis of relative product yields as a function of the relative starting concentrations of styrene and acrylonitrile. We find kg/kA = 0.33 ± 0.04, a result that is consistent with the known selectivity of the 1-phenylethyl radical and that falls within the range of published reactivity ratios for styrene in its copolymerization with acrylonitrile. These results support the use of the mercury method as a source of simple, reliable models for the macroradicals involved in the growth of copolymer chains.

Absolute Rate Constants for the Addition of Benzyl (PhĊH2) and Cumyl (PhĊMe2) Radicals to Alkenes in Solution

“…A better agreement is found with available relative rate constants. For benzene solution at 80°, Giese and Thoma [17] report the ratios 4.1 : 1.3 : 1 .O : 0.24 : 0.048 for (E)-ethene-1,2-dicarbonitrile: 1,l -diphenylethene: acrylonitrile: methyl acrylate: prop-l-ene-2-carbonitrile, whereas we find from Tables 2 and 3 1.0:1.9:1.0:0.20:0.038 at 296 K. Prementine and Tire11 [18] obtained (0.33 f 0.04): 1.0 for the pair styrene: acrylonitrile in CH,Cl, at room temperature and our value is (0.50 f 0.14): 1.0. Finally, at 140" in D M F Terentev et al [19] obtained the ratios 0.29 : 1 .O : 11.9 : 24.0 from a telomerization study of alkenes CH,=CHX with X = CMe,:SiMe,:CO,Me:CN, and we have 0.55:1.0:13.0:66 for the same series ( Table 2).…”

“…The determination of absolute or relative rate constant! ; for low-molecular-weight radicals avoids some of the problems encountered with polymer systems, and these can serve as model for many cases [l] [18]. In fact, we have shown earlier that ratios of absolute rate constants for the addition of CH,CN and CH[,CO,CMe, agree very well with the copolymerization parameters Y, or acrylonitrile and alkyl acrylate [6].…”

Modern aspects of quantitative theory of free-radical copolymerization

“…The direct observation of such a "penultimate effect" in this simple model system speaks in favor of the penultimate model for the description of the copolymerization of styrene and acrylonitrile. Also similar results for this monomer pair were obtained in the model system consisting of 1-phenylethyl [291] and benzene [293] radicals. As for the former one, the estimated value of the reactivity ratio for styrene relative to acrylonitrile was equal to 0.20 + 0.02.…”

“…In the first group [286][287][288][289][290][291][292][293] there were determined the reactivity ratios of the monomer addition to the different low-molecular radicals, the chemical structure of which simulates the structure of the active center at the end of the macroradical. This idea going back to works [286][287] was first used for the polymethacrylonitrile radicals.…”

Recent studies on radical polymerization

“…This coupling is not possible at present for NMR, but is common practice for mass spectrometry. For just this reason we were prompted to explore the use of mass spectrometry coupled with high resolution gas chromatography (GC-MS) in the analysis of an oligomeric mixture for the study of some aspects of the polymerization mechanism Our method of investigation is not completely new: the use of quenchers for studying the structure and fate of primary radicals is reported in the literature (4), as is the study of product distribution in oligomerization (5,6). We took advantage of very efficient separation methods (capillary GC columns) and directed our research to the study of the chain transfer reaction and to the presence of chain-end effects.…”