Synthesis and microstructural characterization of ethylene carbonate-ε-caprolactone/L-lactide copolymers using one- and two-dimensional NMR spectroscopy

Copolymers containing ethylene carbonate (EC) and epsilon-caprolactone (CL)/L-lactide (LA) units of different compositions were synthesized by the ring-opening polymerization method using the SmI2/Sm initiator system. EC was non-homopolymerizable using the same initiator. A maximum of 19 mol % EC was incorporated into the polycaprolactone backbone. The microstructure of these copolymers was analyzed by one- and two-dimensional NMR spectroscopies. The triad sequence distribution centered at CL has been obtained from C-13 NMR spectroscopy. 2D H-1-C-13 HMQC (heteronuclear multiple-quantum correlation) and HMBC (heteronuclear, multiple-bond correlation) spectra were used to confirm the existence of EC as isolated units and CL/LA in the blocks. The complete and correct assignment of peaks in the 13C NMR spectrum of previously reported EC-CL copolymers is also done on the basis of H-1-C-13 HMQC and HMBC spectroscopic techniques.