Study of a solid-state polymerisation reaction: thermal elimination of NaCl from sodium chloroacetate

Abstract

The thermal elimination of sodium chloride from sodium chloroacetate can be accomplished by heating the compound to 150–200 °C. The remaining polyester [‘polyglycolide’, poly(1-oxy-1-oxoethylene)] is obtained in high yield. The reaction was quantitatively studied by thermal analysis (DSC, TG–DTA–mass spectrometry), NMR spectroscopy in solution and in the solid state, X-ray powder diffractometry, electron microscopy and X-ray absorption fine structure spectroscopy (EXAFS). Proton NMR spectroscopy, X-ray diffractometry and chlorine K-edge EXAFS are all well suited to determine the extent of reaction with high accuracy. The reaction proceeds in the solid state in one step without intermediates. Sodium chloride crystals (d= 1–2 µm) are deposited in a polyglycolide matrix while the external crystal morphology is preserved. Combustion of the polyglycolide leaves a sodium chloride framework. Washing out the sodium chloride with water leaves a porous polyglycolide matrix with cubic holes (‘inverse NaCl crystals’).