Epoxidation of bacterial polyesters with unsaturated side chains: IV. Thermal degradation of initial and epoxidized polymers

The thermal decomposition of poly(3-hydroxyoctanoate-co-3-hydroxy-10-undecenoate), PHOU, and the completely epoxidized form of this polymer, poly(3-hydroxyoctanoate-co-3-hydroxy-10,11-epoxyundecanoate), PHOE, have been studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The thermograms of seven different samples of PHOE, which differed in the contents of epoxy, E, units, contained a three-step degradation process, while those of the initial PHOU samples exhibited only one-step degradation process. This degradation behavior of the PHOEs, which have a higher thermal stability as measured by weight loss, is probably controlled by crosslinking reactions of the pendant epoxide groups in the polymer, which occur during the degradation process, and the occurrence of such reactions can be assigned to the exothermic peaks in their DSC thermograms. An isothermal study of these polymers at 250 degrees C for 1 h indicated that the residual weight correlated directly with the amount of epoxide groups in the PHOE samples. (C) 1999 Elsevier Science Ltd. All rights reserved.