The thermochemical behaviour of metal salts (M = Na, Rb, Cs, Ag) of 3-chloro- and 3-bromobutyric acid was studied with respect to the elimination of a metal halide and the formation of poly(3-hydroxybutyrate), P-3HB, a biodegradable polyester. Two possible reaction pathways for this elimination reaction were found. The polycondensation to P-3HB was favoured at lower temperature whereas the formation of volatile crotonic acid and isocrotonic acid was favoured at higher temperature. In the case of silver 3-chlorobutyrate where AgCl was eliminated and P-3HB was the major product. All other combinations of metals and halogen gave only small amounts of polymer. (C) 2008 Elsevier B.V. All rights reserved.