Cyclopolymerization, 13. Cyclocopolymerizations of maleic anhydride with 1,5‐hexadiene and 2,5‐dimethyl‐1,5‐hexadiene

Cyclocopolymerizations of maleic anhydride (1) with 1,5‐hexadiene (2a) and 2,5‐dimethyl‐1,5‐hexadiene (2b) were compared with those of 1 with 1,4‐dienes which have been reported to yield highly cyclized polymers following a bimolecular alternating inter‐intramolecular mechanism. The mole ratio of monomeric units of 1 to those of the dienes in the copolymers was almost 2:1, though it changed slightly with the monomer composition in the feeds. Although the fundamental aspect of the copolymerization of 1 with 1,5‐dienes was found to be similar to that with 1,4‐dienes, the structures of the copolymers are different from those obtained with 1,4‐dienes in that not only pendant double bonds, but also other unsaturations were detected. The unsaturations were formed by combination of propagating radicals with the allyl radical, which is considered to be formed by hydrogen abstraction from the penultimate hexenyl group. A mechanism is proposed to explain the degree of cyclization and the copolymer composition.