Melt mixtures of a polyarylate based on bisphenol A and tere/isophthalates were made with poly(ethy1ene terephthalate), several cyclohexane dimethanol-based polyesters, polycarbonate, and the poly(hydroxy ether) of bisphenol A. The phase behavior was determined using classical methods. With minimum time and temperature exposure, polyarylate exhibits phase separation with poly(ethy1ene terephthalate) (PET) at > 30 wt % PET. With moderate time and temperature exposure, adequate ester exchange occurs with polyarylate/PET blends to yield single-phase behavior. The activation energy of the esterexchange reaction was determined to be 37.0 kcal/mole.
Under minimum time and temperature exposure conditions, miscibility of polyarylate with three different cyclohexane dimethanol-based polyesters was observed. A polyarylate-polycarbonate 5050 mixture was shown to be phase separated under minimum mixing conditions but capable of exchange reactions to yield single-phase behavior with proper time and temperature exposure. Likewise, a 70:30 polyarylate-poly(hydroxy ether of bisphenol A) blend was phase separated as mixed, but with further elevated temperature exposure, a cross-linked single-phase system resulted.
The density versus composition of the polyarylate-PET blends was linear with the phaseseparated systems but exhibited a slight densification with the miscible systems produced by higher temperature exposure. The glass transition of the miscible polyarylate-polyester blends exhibited a significant deviation (lower) than predicted by a linear or Fox equation prediction.
This was attributed to the low value of AC, (specific heat difference between the glass and rubber states) of polyarylate as noted by the Couchman equation to be a major factor in the T, versus composition relationship. The optical characteristics of the blends paralleled the observed phase behavior as single-phase blends were all transparent (in the amorphous state) whereas phase-separated blends were translucent to opaque. These results clearly demonstrate the importance of ester-exchange or transesterification reactions in the phase behavior of blends of polymers capable of these reactions.