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 C), were analyzed using 1H 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