Glass transitions in binary drug + polymer systems

Abstract

To evaluate miscibility, glass transition temperatures Tg have been determined for two binary polymer (Plasdone S-630 copovidone or Eudragit® E) + drug systems as a function of composition. Each polymer serves for encapsulation of the anti-HIV drug Efavirenz. In both systems the Tg vs. drug concentration diagrams are s-shaped. Tgs of Efavirenz + Plasdone mixtures with drug mass fraction below φdrug = 0.6 are above linear values. This implies enhanced thermal and mechanical stability-an advantage for the drug encapsulation. In the other system, a strong negative deviation of Tgs is observed over the entire compositional range and explained by positive excess mixing volumes. Several equations are used to represent Tg vs. composition diagrams, but only one (Brostow et al. Mater Lett 2008; 62:3152) provides reliable results. © 2009 Elsevier B.V. All rights reserved