Sequential reordering in condensation copolymers .3. Miscibility-induced sequential reordering in random copolyesteramides

Binary and ternary blends of poly(butylene terephthalate) (PET), Nylon 66 (PA66), bisphenol-A-polycarbonate (PC) and polyarylate (PAr) have been studied mostly by means of differential scanning calorimetry (DSC) after thermal treatment that enables transesterification. Thus, the entire cycle of sequential reordering is realized, namely: homopolymers --> block copolymer --> random copolymer --> block copolymer. For this purpose the binary PC/PAr and PBT/PA66 blends are annealed in the molten state directly in the calorimeter until complete amorphization (as revealed by DSC). In the first blend the latter is proved by the appearance of a single glass transition temperature T-g and in the second - by the complete diappearance of the crystallization ability. At this stage a third component is added, miscible with one of the starting blend constituents - PBT for the PC/PAr and PAr for the PBT/PA66 blend. Subsequent annealing in the molten state results in amorphization of the PBT-PC-PAr and PBT-PA66-PAr terpolymers, as concluded from the loss of crystallization ability. Further annealing at 280 degrees C and 290 degrees C, respectively, leads to the recovery of the crystallization ability. This is documented by the reappearance of the melting temperature and the crystallinity in the DSC traces taken in heating mode. The crystallinity observed is only achieved during cooling of the melt to room temperature, i.e., crystallization-induced sequential reordering is excluded. It is assumed that the driving force of the observed block regeneration in the melt is the trend of the PET and PAr components of the two randomized copolymers to mix with each other. Mixing presumes the presence of longer PET and PAr sequences. Thus, in addition to the crystallization-induced sequential reordering in condensation copolymers, another example of transreactions is observed in the direction of an entropy decrease. It is called miscibility-induced sequential reordering in random condensation copolymers.