Copolymerization of Maleic Anhydride with Benzofuran, Indole, and Benzothiophene

Maieic anhydride (MAn) forms alternating copolymers with benzofuran (BF), indole, and benzothiophene (BT) under the influence of azobisisoburyronitrile. In all three cases the yield and molecular weight were highest when equimolar amounts of both monomers were used. The association constants of charge-transfer complex formation of MAn with the three comonomers have been measured at various temperatures by NMR. The following values were obtained (at 20°C): MAn-BF ca. 0.01 liter/mole (in cyclohexanone) MAn-indole 0.28 liter/mole (in chloroform) MAn-BT 0.30 liter/mole (in chloroform) The results indicate that the reactivity of the comonomers to form copolymers with MAn is governed by the resonance stabilization of the monomer and to a lesser extent by complex formation. The rate of copolymerization is much higher for the MAn-BF system than for the two other systems. In the former case it is not necessary to invoke charge-complex formation to explain the copolymerization.