INTERACTIONS BETWEEN WATER AND PHARMACEUTICAL POLYMERS DETERMINED BY WATER-VAPOR SORPTION MEASUREMENT AND DIFFERENTIAL SCANNING CALORIMETRY

Interactions between water molecules and various pharmaceutical polyme rs were studied by water vapor sorption and differential scanning calo rimetry (DSC) Water-vapor sorption isotherms at 30 degrees C were dete rmined by gravimetric technique and the monolayer values and moisture content at a relative humidity of 79% were estimated for each sample. The state of the water molecules in moistened polymers was investigate d using DSC and one or two exothermal peaks of water crystallization w ere observed in the DSC cooling curves. The content of non-freezing wa ter, which is restricted by hydrophilic groups in polymer molecules, w as determined from the amount of freezing and total water in the polym er. The amount of water sorbed at high relative humidity and non-freez ing water in DSC measurement correlated to some extent. In hydrophilic polymers having numerous ether linkages, the amount of non-freezing w ater was larger than that predicted from the small amount of sorbed wa ter in the vapor phase.