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BACKGROUND: Modifications of semicrystalline polymers by copolymerization change both the crystallization kinetics and the morphology. Only a few studies concerning ethylene terephthalate (ET)/trimethylene terephthalate (TT) copolyesters have been published. This study extends the work on a series of random aromatic copolyesters. RESULTS: The copolyester was characterized as having 62 mol% TT units and 38 mol% ET units in a random sequence as revealed by NMR. Results of differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) show that the complex melting behavior involves melting-recrystallization-remelting and various lamellar crystals. As the isothermal crystallization temperature increases, the contribution of recrystallization slowly declines, and finally disappears. A Hoffman-Weeks linear plotgives an equilibrium melting temperature of 188.5 • C. The kinetic analysis of the growth rates of spherulites and the change in the morphology from regular to banded spherulites indicate that a regime II → III transition occurs at 135 • C. CONCLUSION: Results of DSC and WAXD demonstrate that this random copolyester is crystallizable. However, its crystallinity is only about 20%.

ABSTRACT:The copolyester was characterized as having 71 mol % trimethylene terephthalate units and 29 mol % ethylene terephthalate units in a random sequence according to the NMR spectra. Differential scanning calorimeter (DSC) was used to investigate the isothermal crystallization kinetics in the temperature range (T c ) from 130 to 170 C. The melting behavior after isothermal crystallization was studied using DSC and temperature-modulated DSC by varying the T c , the crystallization time, and the heating rate. The DSC thermograms and wide-angle X-ray diffraction patterns reveal that the complex melting behavior involves melting-recrystallization-remelting and different lamellar crystals. As the T c increases, the contribution of recrystallization gradually falls and finally disappears. A Hoffman-Weeks linear plot yields an equilibrium melting temperature of 198.7C. The kinetic analysis of the growth rates of spherulites and the change in the morphology from regular to banded spherulites indicate that a regime II!III transition occurs at 148 C.