Radical polymerization of dialkyl muconates (dialkyl 2,4-hexadienoates) was investigated in an isotropic (amorphous) state, that is, solution or bulk polymerization, and in a crystalline state. In the bulk polymerization at 120 °C in the presence of a radical initiator, high molecular weight polymers of more than 105 were obtained in high yields, compared with those in solution polymerization. Three kinds of isomers, cis,cis-, cis,trans-, and trans,trans-muconates, showed similar polymerization reactivities. The microstructure in the polymers was determined by 1H and 13C NMR spectroscopies to be 84−91%, 6−13%, and 2−4% for trans-1,4-, cis-1,4-, and 1,2-structures, respectively, which depended on the polymerization temperature. In contrast with the bulk (in the melt) and solution polymerizations, we discovered that diethyl cis,cis-muconate underwent highly stereospecific polymerization in a crystalline state under UV irradiation via a topochemical polymerization mechanism. The resulting polymer was of ultrahigh molecular weight ([η]) = 103 cm3/g) with high stereoregularity and crystallinity. This polymer has been clarified to be a tritactic polymer, trans-1,4-meso-diisotactic or trans-1,4-meso-disyndiotactic polymer.

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We have investigated the reaction mechanism of the radical polymerization of diethyl (Z,Z)-2,4-hexadienedioate (EMU) in the crystalline state under UV irradiation to yield a polymer of ultrahigh molecular weight with a highly regulated stereochemical structure. The molecular weight of poly(EMU) was estimated to be much higher than 10 6 by gel permeation chromatography and viscometry, irrespective of the polymerization temperature, in contrast to the polymerization rate, which significantly depended on the temperature. The crystal structural change monitored by X-ray diffraction during the polymerization has evidenced the crystal-to-crystal reaction process yielding the poly(EMU) crystals. The results of X-ray diffraction and NMR spectroscopy confirmed that the propagation proceeded under a crystallattice control, leading to the meso-diisotactic-trans-2,5-polymer as a completely regulated structure. The ESR measurement has revealed the radical chain mechanism and the formation of a long-lived propagating radical during the polymerization. In the initiation step of the polymerization, it is supposed that the radical formation is induced not only photochemically but also via a spontaneous process because of the crystal-lattice strain.