Isothermal kinetics of anhydride formation in Eudragit L-100 films determined by reflectance FTir/dsc microspectroscopy

A reflectance Fourier transform infra-red (FTi.r.)/differential scanning calorimetry (d.s.c.) microscopic system was used to investigate the reaction rate and reaction order of anhydride formation in Eudragit L-100 film by isothermal stability study. The accelerated stability testing was performed at 160, 180, 190 and 200 degrees C for 3 h. The changes in three-dimensional reflectance FTi.r. spectra of Eudragit L film with respect to heating time were obtained. The results indicate that the peak areas of three specific i.r. peaks at 1804, 1763 and 1006 cm(-1), assigned to the carbonyl stretching vibration and the asymmetric stretching of C-O-C in Eudragit L-100 film, gradually enlarged with increasing time. The enlargement of these peak areas during the heating process might be attributed to the anhydride formation by inter- or intrapolymer condensation. The order of this isothermal kinetics for anhydride formation in Eudragit L-100 him was 1.85, which might be considered as a second-order reaction, and the activation energy was 51.25 kcal mol(-1).