Cationic copolymerizations of various pairs of benzofuran derivatives have been carried out in CH2Cl2 using SnCl4–CCl3CO2H (2: 1) as catalyst at 0 °C. Effects of 2- and 3-methyl substitutions on the monomer reactivity ratio suggested that the polymeric cation adds at the 2-carbon of benzofuran. Analysis of the effects of 5- and 6-substituents on the reactivity revealed that the transmission efficiency of electronic effects through the two paths, the bonds 8–3 and 9–1–2, is comparable in magnitude. It was concluded that the transition state of the propagation step closely resembles a bridged carbonium ion intermediate.
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Okuyama et al. (1974) studied this question.
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