Thermogravimetric investigation of two classes of block copolymers based on poly(lactic-glycolic acid) and poly(ε-caprolactone) or poly(ethylene glycol)

The thermogravimetric analysis (TGA) of two classes of multi-block copolymers based on poly(D,L-lactic-glycolic acid) (PLGA) and diol-terminated poly(epsilon -caprolactone) (PCDT) or poly(ethylene glycol) (PEG) segments is reported. These materials, having the structure of poly(ester-carbonate)s, were synthesized by a chain extension reaction. The influence of the length of PCDT or PEG segments and of the molar ratio Of D,L-lactic acid (LA) and glycolic acid (GA) residues on thermal stability in air and nitrogen atmosphere has been investigated. For comparison purposes the degradation behaviour of starting oligomers was also studied. TGA under nitrogen shows two degradation processes that can be ascribed to the PLGA and PCDT or PEG segments, respectively. In addition, the thermal stability increases with the LA content in the PLGA blocks. In the tests run under air two degradation steps have also been observed, though the former occurs in general at higher temperatures. (C) 2001 Elsevier Science Ltd. All rights reserved.