The slow molecular dynamics in amorphous probucol

• The slow mobility in an amorphous pharmaceutical ingredient is characterized.
• The fast secondary, the Johari–Goldstein and the main relaxations are identified.
• The activation energy and entropy of the motional modes are determined.
• The fragility index of probucol was calculated as m∼60 using different methods.
• The thermal behavior is analyzed from DSC results.

The slow molecular mobility in the active pharmaceutical ingredient probucol was studied by Thermally stimulated depolarisation currents (TSDC) in the temperature region between −130 and 50 °C. The distribution of relaxation times was characterized for the secondary relaxations and for the glass transition relaxation. Based on aging results we were able to draw distinctions between the fast secondary relaxation on the one hand, and the slow-β or Johari–Goldstein relaxation on the other. The steepness index of probucol was calculated from the temperature dependent relaxation time of the glass transition and using methods based on the influence of the scanning rate on the glass transition signal (in DSC and TSDC). The obtained values show some scattering but they are in the frontier between the fragile and strong behaviors.

Figure optionsDownload as PowerPoint slide