Summary: To clarify the cationic copolymerization behavior of epoxide and cyclic carbonate, the copolymerization behavior of glycidyl phenyl ether (GPE) with seven‐membered cyclic carbonate (7CC) was carried out using methyl trifluoromethanesulfonate (MeOTf) as a cationic initiator. The addition of 7CC accelerated the consumption rate of GPE, and the resulting copolymers were richer in 7CC‐derived unit compared to the feed ratio of 7CC. During the copolymerization, a large amount of five‐membered cyclic carbonate having a phenoxymethyl group (PM‐5CC) was produced as a by‐product, which suggests the corresponding spiroorthocarbonate was formed as an intermediate and that residual oxytetramethylene (OTM) unit was incorporated into the copolymer sequence. From 1H NMR analysis, it was found that the copolymers had a statistically random sequence consisting of GPE, 7CC, and OTM units.
