Low and medium molecular weight copolymers constituted by glycolide and p-dioxanone units have been synthesized by a ring-opening polymerization. The p-dioxanone monomer was obtained from (2-hydroxyethoxy)acetate or by thermal depolymerization of poly(p-dioxanone). H-1 and C-13 NMR spectra were highly sensitive to the chemical sequences. which were effectively assigned by considering the data from samples with different compositions, and the acquisition of heteronuclear H-1 and C-13 NMR-correlated spectra. End groups were also identified, allowing methylene protons of sequences involving up to two glycolide units to be distinguished. These data seem basic to analyze degradation products or the influence of thermal treatments in chain microstructure. Glycolide/p-dioxanone copolymers are an interesting system because changes oil chemical sequences can easily occur due to a depolymerization reaction that eliminates p-dioxanone residues. Furthermore, depending on the polymerization conditions, the occurrence of transesterification reactions may be highly significant These reactions have a great impact in properties such as the melting temperature and can be easily quantified by NMR spectroscopy because of the occurrence of a new chemical sequence. (C) 2009 Wiley Periodicals, Inc J Polym Sci Part A Polym Chem 47 6758-6770, 2009