COPOLYMERS OF 1,5-DIOXEPAN-2-ONE AND L-SYNTHESIS OR D,L-DILACTIDE-SYNTHESIS AND CHARACTERIZATION

The copolymerization of 1,5-dioxepan-2-one (DXO) with L- or D,L-dilactide in bulk has been studied, using stannous-2-ethylhexanoate as the initiator. The copolymers were characterized using H-1- and C-13-NMR spectroscopy, and DSC-analysis. The molecular weight of the copolymers was measured by SEC, viscometry and light-scattering techniques. The reactivity ratios of the copolymer system were calculated using the Kelen-Tudos method to be r1 (DXO) = 0,1 and r2 (dilactide) = 10. No racemization seems to have taken place during polymerization as shown by the absence of stereochemical splittings in the C-13-NMR spectra of the L-dilactide homopolymer. The ability of the L-LA/DXO copolymer to crystallize seems to be retained despite substantial amounts of 1,5-dioxepan-2-one in the composition. H-1- and C-13-NMR spectra indicate ring-opening of the monomers by alkyl-oxygen cleavage.