This article deals with the polyaddition of a novel bis(seven-membered cyclic carbonate), 1,2-bis[3-(1,3-dioxepan-2-one-5-yl)-propyltbio]ethane, with the diamines 4,9-dioxa-1,12-dodecanediamine and p-xylylenediamine. The polyaddition was carried out at 30-70 degreesC for 6-24 h in dimethyl sulfoxide to obtain the corresponding polyhydroxyurethanes with number-average molecular weights of 10,900-35,700 in good yields. The reaction of a monofunctional seven-membered cyclic carbonate, 5-allyl-1,3-dioxepan-2-one (7CC), with monoamines was also carried out to examine the reactivity in comparison with that of six- and five-membered cyclic carbonates. The reaction rate constants of 7CC with n-hexylamine and benzylamine were estimated to be 48.5 and 11.0 L/mol(.)h, respectively, in dimethyl sulfoxide-d(6) (initial reagent concentration = 1 M) at 30 degreesC. The seven-membered cyclic carbonate ring was 2.98 and 5.82 kcal/mol more strained than those of the six- and five-membered cyclic carbonates, respectively, according to a semiempirical molecular orbital calculation with the PM3 Hamiltonian.