Donor–acceptor complexes in copolymerization. LVIII. Alternating diene–dienophile copolymers. 12. Structure of furan–maleic anhydride copolymers prepared from the monomers and the diels-Alder adduct

The copolymerization of furan with maleic anhydride in the presence of a perester or azobisiso-butyronitrile at 50 or 70°C yields an unsaturated equimolar, alternating copolymer in which the furan units have 3,4 unsaturation and 2,5 linkages. The furan–maleic anhydride Diels-Alder adduct undergoes retrograde dissociation in solution at 70°C and, in the presence of radical catalysts, yields the same unsaturated alternating copolymer as is obtained from the monomers. The adduct undergoes homopolymerization in the presence of a rapidly decomposing perester at 50°C to yield a saturated polymer having a rearranged structure containing 3-oxabicyclo2.2.1]heptane-5,6-dicarboxylic anhydride repeating units with 2,7 linkages.