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

The thermogravimetric analysis (TGA) of two classes of multi-block copolyme rs based on poly(D,L-lactic-glycolic acid) (PLGA) and diol-terminated poly( epsilon -caprolactone) (PCDT) or poly(ethylene glycol) (PEG) segments is re ported. These materials, having the structure of poly(ester-carbonate)s, we re synthesized by a chain extension reaction. The influence of the length o f PCDT or PEG segments and of the molar ratio Of D,L-lactic acid (LA) and g lycolic acid (GA) residues on thermal stability in air and nitrogen atmosph ere has been investigated. For comparison purposes the degradation behaviou r of starting oligomers was also studied. TGA under nitrogen shows two degr adation processes that can be ascribed to the PLGA and PCDT or PEG segments , respectively. In addition, the thermal stability increases with the LA co ntent 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 temp eratures. (C) 2001 Elsevier Science Ltd. All rights reserved.