Unlike previous attempts, the entire cycle of melting-and crystallization-induced reordering is realized in binary polymer blends in the following order: two homopolymers + block copol mer + random copolymer + block copolymer. Blends of poly(ethy1ene terephthalate) by (PET) and bisphenol-Npolycarbonate (PC) as well as PET/polyarylate (PAr) blends, are annealed directly in a differential scanning calorimeter at 280°C for various times. Scanning the samples in the heating mode reveals the complete disappearance of crystallization or melting in the blends where the ratio of PETPC repeating units is less than 5.7/1.0. Such an amorphization is attributed to the formation of random copolymers. This statement is confirmed by NMR measurements, by the observation of one glass transition temperature Tg in the range between the initial two Tgs, and by solubility tests. Once randomized, annealing the samples at 235 "C and 245 "C, i. e., below melting of PET, results in a Tg shift toward the Tg of PET as well as in reappearance of melting. This effect is accompanied by an eight-fold crystallinity increase in the equimolar blend, as compared to the randomized sample. The regenerated crystallization ability is explained by restoration of the blocks. According to previous findings, it is concluded that the considerable entropy increase is the main driving force of randomization. The rival trend to the formation of a block copolymer by sequential reordering is driven by the crystallization of PET blocks formed. The conclusion that the observed changes in the crystallization ability and Tg-values are based on sequential reordering is supported by experiments with samples containing increased amounts of transesterification catalyst leading to a much faster appearance of these changes. No randomization is observed with the blend composition ratio of repeating units PETPC > 5.7/1.0. When the annealing is performed for 300 min at 165 "C, where no significant exchange reactions are expected to occur, no restoration of the crystallization ability is observed.

A 50/50 (weight ratio (38/62 mole ratio referred to repeating units)) blend of poly(butylene terephthalate) (PBT) and polyarylate (PAr), was studied by means of thermal, solubility, X-ray and nuclear magnetic resonance techniques after annealing procedures that enable transesterification. Prolonged thermal treatment at 290 "C gives rise to a copolymer that no longer reveals melting or crystallization. In accordance with previous reports, this effect is attributed to the formation of a random copolymer. Additional annealing of such samples at the relatively low temperature of 140°C results in the reappearance of melting endotherms in the differential scanning calorimetry curves. This effect is explained by crystallization-induced sequential reordering from random to block copolymer by means of transreactions. In that way a PBTPAr blend was shown to be another polymer system, along with poly(ethy1ene terephthalate) (PET)/polycarbonate (PC) and PETPAr blends, in which the entire cycle is realized, from two homopolymers via a block-and random copolymer to a block copolymer. The unusually low temperature at which the crystallization-induced sequential reordering to block polymers takes place is explained by the miscibility of PBT and PAr which enables transreactions to take place in the bulk.

Binary and ternary blends of poly(buty1ene terephthalate) (PBT), 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 PCPAr and PBTPA66 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 Tg and in the secondby 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 PCPAr and PAr for the PBTPA66 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°C and 290 "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 PBT and PAr components of the two randomized copolymers to mix with each other. Mixing presumes the presence of longer PBT 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. a) part 2: cf. ref.37) b, Permanent address: Laboratory on Structure and Properties

No abstract

SUMMARY An equimolar blend of poly(ethy1ene terephthalate) (PET)' and bisphenol-A-polycarbonate (PC)d is studied by dynamic-mechanical thermal analysis (DMTA) and X-ray scattering after thermal treatment that enables transesterification. As demonstrated by wide-angle X-ray scattering (WAXS) measurements, prolonged thermal treatment at 280°C gives rise to a copolymer that no longer reveals melting or crystallization. In accordance with previous reports, this effect is attributed to the formation of a random copolymer. Additional annealing of such samples below the melting temperature of PET results in restoration of the crystallization ability. This effect is explained by crystallization-induced sequential reordering from random to block copolymer by means of transreactions which closes the cycle of transformations from two homopolymers via block-and random copolymer back to a block copolymer. The behavior of the amorphous phases is studied by means of DMTA demonstrating that their glass transition temperatures Tg's vary in accordance with the crystallinity changes. The random copolymer is characterized by a more or less homogeneous amorphous phase. In contrast to this, the mechanical mixture and the two block copolymers (the initial and that with the restored blocky structure) show DMTA peaks of two amorphous phases, clearly separated and with distinct individual Tg's. Viscosity measurements also demonstrate that the random copolymer significantly differs in its viscosity as compared to all other samples. These results represent a further evidence for the effect of block restoration via crystallization-induced sequential reordering.