Hydrolytic degradation of copolymers based on l-lactic acid and bis-2-hydroxyethyl terephthalate

Abstract The current demand for environmentally degradable copolymers has led to the use of novel degradable copolyesters. A series of copolyesters based on bis-2-hydroxyethyl terephthalate and l -lactic acid oligomers were synthesized by melt polycondensation [Olewnik E, Czerwinski W, Nowaczyk J, Sepulchre M-O, Tessier M, Salhi S, et al. Synthesis and structural study of copolymers of l -lactic acid and bis(2-hydroxyethyl terephthalate). Eur Polym J, in press]. Hydrolytic degradation of copolymers containing 16.8–52.9 mole ratio of l -lactic acid units was carried out in two buffered solutions at two different temperatures: phosphate buffer solution (pH 7.40) at 45 °C and phosphate–citric buffer solution (pH 7.35) at 60 °C. Degradation of copolyesters was studied by incubating samples in powder form in a concentrated solution from 30 to 180 days. The copolymers were characterized by various analytical techniques. The thermal properties, morphology and structural changes during controlled hydrolysis were studied by scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) for determining melting points, heats of melting and decomposition temperatures of investigated copolyesters. 1 H NMR spectroscopy was used to observe the decomposition of the polyesters.