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.
