Alternating copolymerization of benzofuran with crotononitrile and α-chloroacrylonitrile

The copolymerizations of benzofuran with α,α- or α,β-disubstituted acrylic monomers were studied. The alternating copolymer of benzofuran and crotononitrile was prepared in the presence of an excess amount of crotononitrile with respect to benzofuran, ethylaluminum dichloride, and azobisisobutyronitrile. The intrinsic viscosity of copolymers was 0.1–0.2 dl/g. Crotononitrile is known to possess a polar carbon–carbon double bond from ¹³C-NMR spectroscopy but the alternating copolymerizability with benzofuran is low. It was found that the order of alternating copolymerizability of acrylic monomers is as follows: This fact may be attributed to the steric hindrance of the β-methyl of crotononitrile. The induced shifts by complexation with ethylaluminum dichloride on ¹³C-NMR spectra of the two isomers of crotononitrile are almost same but the copolymerizability of cis isomer is higher than that of trans isomer. α-Chloroacrylonitrile shows the highest alternating copolymerizability with benzofuran in the presence of weak Lewis acid such as ethoxyaluminum chloride. Alternating copolymerizability of acrylic monomers seems to be in proportion to their e value. The reactivity of cis- and trans-crotononitrile may depend on the nature of a ternary complex composed of aluminum compound, crotononitrile, and benzofuran.