Abstract
Kinetics of the reactions of benzhydryl cations with 2,4,6-trimethylstyrene have been performed to determine its nucleophilicity parameters N = 0.68 and s = 1.09, which are comparable to styrene and considerably less nucleophilic than 4-methylstyrene, indicating the retarding effect of the ortho methyl groups. Kinetic investigations of the reactions of the 2,4,6-trimethylstyryl cation 6+ and the corresponding dimer 7+ with the reference nucleophile 2-chloropropene allow us to calculate the closely similar electrophilicity parameters E(6+) = 6.04 and E(7+) = 6.16 which are considerably lower than that of the styryl cation (E = 9.6). As a consequence, the propagation rate constant of the cationic polymerization of 2,4,6-trimethylstyrene is considerably lower than that of styrene. Substituting these values into the correlation log k20 °C = s(N + E) yields a propagation rate constant of 3 × 107 M-1 s-1, which has to be considered an upper limit because extra steric strain generated in the reaction of 7+ with ...
Published Version
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