MISCIBILITY AND TRANSESTERIFICATION OF PHENOXY WITH BIODEGRADABLE POLY(3-HYDROXYBUTYRATE)

The miscibility and transesterification of poly(hydroxyl ether of bisp henol A) (phenoxy) and poly(3-hydroxybutyrate) (PHB) were investigated by means of differential scanning calorimetry (DSC) and Fourier trans form IR spectroscopy (FTi.r.). The blends, prepared by casting from a dimethylformamide solution at 80 degrees C and drying in vacuum at 80 degrees C, heated from room temperature to 180 degrees C at a rate of 10 degrees C min(-1), are miscible at 180 degrees C when the PHB conte nt is less than about 20 wt.% and almost immiscible when the PHB conte nt is over 20 wt.%. The FTi.r. spectra reveal that the PHB content in the THF soluble fraction of the blends containing 30 wt.% PHB annealed at 180 degrees C increases with increasing annealing time. Both the e xtraction and the FTi.r. experiments indicate that transesterification occurs between phenoxy and PHB. When the transesterification is compl ete, hence when the annealing time is long enough, a single phase is f ormed. During transesterification, the number of non-hydrogen-bonded O H groups of phenoxy first increases, passes through a maximum and then decreases with increasing annealing time at 180 degrees C, becoming n egligible once a single phase is formed. An explanation is proposed fo r this behavior. (C) 1998 Elsevier Science Ltd. All rights reserved.