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This communication shows that thermal degradation of poly(3-hydroxybutyrate)s (PHBs) is induced by carboxylate groups via a newly proposed E1cB mechanism. In PHBs with end groups in the form of carboxylic acid salts with Na+, K+, and Bu4N+ counterions, the proposed mechanism explains the dependence of thermal stability on the size of the counterion. The degradation via intermolecular alpha-deprotonation by carboxylate is suggested to be the main PHB decomposition pathway at moderate temperatures. The results of the present study show the ability to control the degradation and stability of poly(3-hydroxybutyrate)s as well as of their blends via chemical structure and concentration of the carboxylate polymer end groups.

Degradation of poly[(1,4-butylene terephthalate)-co-(1,4-butylene adipate)] (Ecoflex, BTA) monofilaments (rods) in standardized sandy soil was investigated. Changes in the microstructure and chemical composition distribution of the degraded BTA samples were evaluated and changes in the pH and salinity of postdegradation soil, as well as the soil phytotoxicity impact of the degradation products, are reported. A macroscopic and microscopic evaluation of the surface of BTA rod samples after specified periods of incubation in standardized soil indicated erosion of the surface of BTA rods starting from the fourth month of their incubation, with almost total disintegration of the incubated BTA material observed after 22 months. However, the weight loss after this period of time was about 50% and only a minor change in the M(w) of the investigated BTA samples was observed, along with a slight increase in the dispersity (from an initial 2.75 up to 4.00 after 22 months of sample incubation). The multidetector SEC and ESI-MS analysis indicated retention of aromatic chain fragments in the low molar mass fraction of the incubated sample. Phytotoxicity studies revealed no visible damage, such as necrosis and chlorosis, or other inhibitory effects, in the following plants: radish, cres, and monocotyledonous oat, indicating that the degradation products of the investigated BTA copolyester are harmless to the tested plants.