Thermal degradation of poly[(R)-3-hydroxybutyrate], poly[epsilon-caprolactone], and poly[(S)-lactide]

Thermal degradations of poly[(R)-3-hydroxybutyrate] (PHB), poly[epsilon-caprolactone] (PCL), and poly[(S)-lactide] (PLA) were investigated under both isothermal and non-isothermal conditions. In isothermal degradation experiments, the three polyesters showed quite different time-dependent profiles of weight loss and the number-average degree of polymerization, reflecting their different degradation mechanisms. Thermogravimetric analysis and pyrolysis coupled with GC/MS suggest that PHB is degraded by a random chain scission (cis-elimination), while PCL is degraded by an unzipping depolymerization from the hydroxyl end of the polymer chains. In contrast, the thermal degradation behavior of PLA was very complex because various reactions occurred concurrently. (C) 2002 Elsevier Science Ltd. All rights reserved.