Anionic equilibrium polymerization behavior of several six-membered cyclic carbonates was
examined. The conversions of the monomers reached a constant below 100%, and the final conversion
decreased in the order of 1,3-dioxan-2-one (1) > 5,5-dimethyl-1,3-dioxan-2-one (2) > 5,5-diethyl-1,3-dioxan-2-one (3) ≥ 5-methyl-5-phenyl-1,3-dioxan-2-one (4) > 5-ethyl-5-phenyl-1,3-dioxan-2-one (5). The reactions
of 2,2-disubstituted-1,3-propanediols were carried out with phosgene dimer to find that the cyclic carbonate
(5) was formed quantitatively in the reaction of 2-ethyl-2-phenyl-1,3-propanediol, while the corresponding
polycarbonate was formed in the reaction of 2,2-diethyl-1,3-propanediol in 24% yield besides 3.
Thermodynamic parameters were estimated in the anionic ring-opening polymerizations of cyclic
carbonates (1−5) by Dainton's equation. The obtained ΔH
p value in the ring-opening polymerization of
each cyclic carbonate reflected the polymerizability. Molecular orbital calculations of the model compounds
of the polymers were carried out to find that the polymerizabilities of the cyclic carbonates correlated
with the stabilities of the corresponding polymer structures. The concentrations of the monomers formed
in the depolymerizations well agreed with the equilibrium monomer concentrations in the anionic ring-opening polymerizations.
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