Hydrogen bonding interactions and miscibility studies of poly(amide)/poly(vinyl pyrrolidone) blends containing mangiferin

Miscibility studies of amorphous poly(amide)/poly(vinyl pyrrolidone) (PA/PVP) blends containing a crystalline phytochemical called “mangiferin” have been carried out using differential scanning calorimetry, Fourier transformed infrared spectroscopy and polarized optical microscopy. The binary blends of PA/PVP prepared from dimethylsulfoxide solutions were found to be completely miscible showing a systematic movement of a single glass transition temperature over the entire composition range. The FTIR study indicated the occurrence of cross-hydrogen bonding interactions between PA and PVP, which may be responsible for complete miscibility of the PA/PVP pair. Moreover, cross-hydrogen bonding promotes miscibility in binary blends of PA/mangiferin and PVP/mangiferin. However, the addition of mangiferin to PA/PVP blends has resulted in liquid–liquid phase separation between PA/mangiferin and PVP/mangiferin phases due to the preferential affinity of mangiferin to PVP than to PA. With increasing mangiferin concentration, liquid–liquid phase segregations occur between PA + mangiferin and PVP + mangiferin phases in addition to the solid–liquid phase transition of mangiferin crystals. Lastly, a ternary morphology phase diagram of the PA/PVP/mangiferin blends was established, which exhibited various coexistence regions such as isotropic, liquid + liquid, liquid + crystal, liquid + liquid + crystal, and solid crystal regions.