Synthesis and characterization of random copolyesters of ε-caprolactone and 2-oxepane-1,5-dione

2-Oxepane-1,5-dione (OPD) has been synthesized by the Baeyer-Villiger oxidation of 1,4-cyclohexanedione and copolymerized with epsilon-caprolactone. This random copolymerization has been initiated by different metal derivatives, i.e., tin octanoate, dibutyltin dimethoxide, and aluminum isopropoxide. Dibutyltin dimethoxide is the preferred initiator, and the course of polymerization is controlled by the competition of the ketone of OPD and the ester of the lactones for coordination to the initiator. Semicrystalline copolymers are formed, whose the randomness has been confirmed by DSC, H-1 NMR, and C-13 NMR analysis. A single melting temperature (T-m) has been observed, which varies regularly and monotonically with the OPD content as result of a cocrystallization phenomenom. The single glass transition temperature (T-g) obeys the Fox equation.