Solid-State Polymerization Reaction by Combined In-Situ X-ray Diffraction and X-ray Absorption Spectroscopy (XRD−EXAFS)

Abstract

The solid-state polymerization reaction of sodium bromoacetate has been studied with combined in situ X-ray diffraction and X-ray absorption spectroscopy (XRD−EXAFS). This elimination reaction leads quantitatively to sodium bromide and poly(hydroxyacetic acid), polyglycolide. Both XRD and EXAFS data have been quantitatively analyzed to yield the molar fractions of educt and products during the reaction. Results of both methods confirm that the reaction is occurring without a crystalline, liquid, or amorphous intermediate in one single step. Sodium bromide is precipitated in small crystals in the polymeric matrix. The growth of the microcrystals could be followed by analyzing the XRD line width during the reaction, an observation that is corroborated by scanning electron microscopy. This allows a control of the pore size distribution of the obtained material by variation of the reaction temperature.