SOLID STATE POLYMERIZATION REACTIONS IN ALKALI SALTS OF HALOGENOCARBOXYLIC ACIDS Oliver Herzberg, Holger Kirschnick and Matthias Epple, Institute of Inorganic and Applied Chemistry, University of Hamburg, Martin-Luther- King-Platz 6, D-20146 Hamburg, Germany

Thermal oligomerization and polymerization takes place in alkali salts of halogenocarboxylic acids, e.g.: NaOOC-CH(Cl)-CH²-CH³ ---> NaCl + 1/n (-OOC-CH(CH²CH³)-)n This reaction leads to pharmaceutically and technically interesting oligomers and polymers which were characterized by gel permeation chromatography (GPC). These polyesters of hydroxycarboxylic acids are easily biodegradable in the body and the environment. The precursor salts are metastable and sometimes difficult to prepare, because some are highly unstable towards elimination of HCl to alkenoic acid salts. Some were prepared as for the first time, although reported as "unstable at room temperature" in the literature. The salts were characterized by powder diffractometry, thermal analysis and solid-state NMR. The above polymerization reaction was followed by in situ X-ray powder diffractometry and thermal analysis in order to gain insight into the mechanism of this solid-state reaction. It is remarkably exothermic which underscores the metastable character of the educt substances.

M.Epple, L. Troeger, J. Chem. Soc., Dalton Trans., 1996, 11-16.