A Convenient Route to PHB Macromonomers via Anionically Controlled Moderate-Temperature Degradation of PHB

The degradation of poly(3-hydroxybutyrate)s in homo- and heterogeneous mixtures with selected salts of organic and mineral acids was investigated. Nonvolatile degradation products, of processes conducted at moderate temperatures (150-170 degrees C), were analyzed using (1)H NMR. Analysis of results revealed a significant decrease in poly([R]-3-hydroxybutyrate) (PHB) thermal stability in the presence of acetic acid and carbonic acid salts of alkali metals (Cs, K, Li) as well as a less substantial effect with respect to bivalent metal (Ca, Mg, Zn) salts. This significant decrease in PHB thermal stability in the presence of salts of weak Bronsted-Lowry acids can be explained in terms of an anionic degradation reaction proceeding via an E1cB mechanism. Furthermore, continuous poly(3-hydroxybutyrate) controlled degradation was developed by a moderate-temperature process using carbonic acid salts as "initiators" of anionic degradation. Foamed PHB macromonomers, bearing one crotonate terminal group, were obtainable via a reactive extrusion process. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 5490-5497, 2010