SEQUENTIAL REORDERING IN CONDENSATION COPOLYMERS .1. MELTING-INDUCED AND CRYSTALLIZATION-INDUCED SEQUENTIAL REORDERING IN IMMISCIBLE BLENDSOF POLY(ETHYLENE-TEREPHTHALATE) WITH POLYCARBONATE OR POLYARYLATE

Unlike previous attempts, the entire cycle of melting- and crystalliza tion-induced reordering is realized in binary polymer blends in the fo llowing order: two homopolymers --> black copolymer --> random copolym er --> block copolymer. Blends of poly(ethylene terephthalate)(b)) (PE T) acid bisphenol-A/polycarbonate (PC) as well as PET/polyarylate (PAr ) blends, are annealed directly in a differential scanning calorimeter at 280 degrees C for various times. Scanning the samples in the heati ng mode reveals the complete disappearance of crystallization or melti ng in the blends where the ratio of PET/PC repeating units is less tha n 5.7/1.0. Such an amorphization is attributed to the formation of ran dom copolymers. This statement is confirmed by NMR measurements, by th e observation of one glass transition temperature T-g in the range bet ween the initial two T(g)s, and by solubility tests. Once randomized, annealing the samples at 235 degrees C and 245 degrees C, i.e., below melting of PET, results in a T-g shift toward the T-g of PET as well a s in reappearance of melting. This effect is accompanied by an eight-f old crystallinity increase in the equimolar blend, as compared to the randomized sample. The regenerated crystallization ability is explaine d by restoration of the blocks. According to previous findings, it is concluded that the considerable entropy increase is the main driving f orce of randomization. The rival trend to the formation of a block cop olymer by sequential reordering is driven by the crystallization of PE T blocks formed. The conclusion that the observed changes in the cryst allization ability and T-g-values are based on sequential reordering i s supported by experiments with samples containing increased amounts o f transesterification catalyst leading to a much faster appearance of these changes. No randomization is observed with the blend composition ratio of repeating units PET/PC > 5.7/1.0. When the annealing is perf ormed for 300 min at 165 degrees C, where no significant exchange reac tions are expected to occur, no restoration of the crystallization abi lity is observed.