The incorporation or encapsulation of a drug in a biodegradable polymer can greatly enhance the controlled release of the drug, and thereby increase its efficacy. The use of supercritical carbon dioxide (scCO2 ) to lower the glass transition temperature of the polymer, thereby allowing the drug to diffuse into the polymer, offers significant advantages in such applications [1-3]. Chow's theoretical relation can be used to predict variations of the glass transition temperature when diluents are added. However, its application is limited to regions near and above the critical point of the diluent fluid [4]. Recently, Ozkan and Teja, [5] described a thermodynamic model (modified g-ARTL) for associating polymer solutions that accounts for specific solute-solvent interactions in supercritical CO2 –polymer solutions. In the present work, we extend the application of their model to the prediction of glass transition temperatures by combining the modified g-ARTL equation with the DiMarzio criterion [6]. In situ Fourier transform IR (FT-IR) spectroscopy is employed to investigate the interaction of CO2 with the polymers of interest, and shifts in the spectra of polymers exposed to CO2 are used to obtain one of the model parameters. In addition, in situ high pressure DSC measurements on select biopolymers are employed to to measure the effect of the dissolved diluent on glass transition temperature.

[1] Mooney, D.J.; Baldwin, D.F.; Suh, N.P.; Vacanti, J.P.; Langer, R., Biomaterials 17, 1417, (1996). [2] Harris, L.D.; Kim, B.S.; Mooney, D.J., J. Biomed. Mater. Res. 42, 396, (1998). [3] Hile, D. D.; Amirpour, M. L.; Akgerman, A.; Pishko, M. V., J. of Controlled Release, 66, 177, (2000). [4] Chow, T. S., Ferroelectrics, 30 (1-4), 139, (1980). [5] I. Ozkan, A.S. Teja, Fluid Phase Equil. 228-229, 487 (2005). [6] Gibbs, J. H.; DiMarzio, E. A., J. Chem. Phys. 28, 373, (1958).