SOLID-STATE POLYMERIZATION REACTION BY COMBINED IN-SITU X-RAY-DIFFRACTION AND X-RAY-ABSORPTION SPECTROSCOPY (XRD-EXAFS)

The solid-state polymerization reaction of sodium bromoacetate has bee n studied with combined in situ X-ray diffraction and X-ray absorption spectroscopy (XRD-EXAFS). This elimination reaction leads quantitativ ely to sodium bromide and poly(hydroxyacetic acid), polyglycolide. Bot h XRD and EXAFS data have been quantitatively analyzed to yield the mo lar fractions of educt and products during the reaction. Results of bo th methods confirm that the reaction is occurring without a crystallin e, liquid, or amorphous intermediate in one single step. Sodium bromid e is precipitated in small crystals in the polymeric matrix. The growt h of the microcrystals could be followed by analyzing the XRD line wid th during the reaction, an observation that is corroborated by scannin g electron microscopy. This allows a control of the pore size distribu tion of the obtained material by variation of the reaction temperature .