DIELECTRIC AND THERMODYNAMIC PROPERTIES OF BIODEGRADABLE POLY(D,L-LACTIDE-CO-GLYCOLIDE) AND THE EFFECT ON THE MICROENCAPSULATION AND RELEASE OF CAPTOPRIL

The mechanical and dielectric properties of three kinds of poly(lactic acid-co-glycolic acid) (PLG) with different molecular weights and pol ydispersities fractioned by ultrafiltration were investigated by dynam ic mechanical thermal analysis (DMTA) and dielectric measurement. All samples showed typical behaviour of amorphous polymer under different fields. Two relaxation processes were found, a secondary relaxation in glassy state at low temperature and a glass transition relaxation. Th e molecular weights and polydispersities of PLGs influenced significan tly both relaxation, especially the relaxation strength and location. The strength of secondary relaxation was reduced and the glass transit ion shifted to a higher temperature when the molecular weight of PLG i ncreased and the polydispersity decreased. The shift of glass transiti on temperature (Tg) might decrease the motion of the macromolecules an d resulted in a higher moduli of rubbery PLG at the temperature of the drug system (37 degrees C) and lowered the diffusivity of the drug in polymeric matrix and then the initial burst and fast diffusional rele ase of captopril from commercial PLG were improved.