SEQUENTIAL REORDERING IN CONDENSATION COPOLYMERS, 4 - CRYSTALLIZATION-INDUCED SEQUENTIAL REORDERING IN POLY(ETHYLENE TEREPHTHALATE) POLYCARBONATE COPOLYMERS AS REVEALED BY THE BEHAVIOR OF THE AMORPHOUS PHASES/

An equimolar blend of poly(ethylene terephthalate) (PET)(c) and bisphe nol-A-polycarbonate (PC)(d) is studied by dynamic-mechanical thermal a nalysis (DMTA) and X-ray scattering after thermal treatment that enabl es transesterification. As demonstrated by wide-angle X-ray scattering (WAXS) measurements, prolonged thermal treatment at 280 degrees C giv es rise to a copolymer that no longer reveals melting or crystallizati on. In accordance with previous reports, this effect is attributed to the formation of a random copolymer. Additional annealing of such samp les 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 h omopolymers via block-and random copolymer back to a block copolymer. The behavior of the amorphous phases is studied by means of DMTA demon strating that their glass transition temperatures T-g's vary in accord ance with the crystallinity changes. The random copolymer is character ized by a more or less homogeneous amorphous phase. In contrast to thi s, the mechanical mixture and the two block copolymers (the initial an d that with the restored blocky structure) show DMTA peaks of two amor phous phases, clearly separated and with distinct individual T-g's. Vi scosity measurements also demonstrate that the random copolymer signif icantly differs in its viscosity as compared to all other samples. The se results represent a further evidence for the effect of block restor ation via crystallization-induced sequential reordering.