Poly(ethylene succinate) (PES) and its copolyesters that contain 7, 10, or 48 mol % butylene succinate (BS) were synthesized through a direct polycondensation reaction with titanium tetraisopropoxide as the catalyst. Measurements of intrinsic viscosity (1.08-1.27 dL/g) proved the success of the preparation of polyesters with high molecular weights. The compositions and the sequence distributions of the copolyesters were determined from 1 H and 13 C NMR spectra. The distributions of ethylene succinate and BS units were found to be random. Their thermal properties were elucidated using a differential scanning calorimeter (DSC) and a thermogravimetric analyzer. No significant difference exists among the thermal stabilities of these polyesters. All of the copolymers exhibit a single glass transition temperature. Wide-angle X-ray diffractograms (WAXD) were obtained from polyesters that were crystallized isothermally. The DSC thermograms and WAXD patterns indicate that the incorporation of BS units into PES significantly inhibits the crystallization behavior of PES. The heat of fusion of ideal PES crystals is 163 J/g, as determined by the depression of the melting point of PES crystals in acetophenone.
ABSTRACT:The copolyester was synthesized and characterized as having 92.7 mol % ethylene succinate units and 7.3 mol % butylene succinate (BS) units in a random sequence, as determined by the use of nuclear magnetic resonance. Isothermal crystallization kinetics of this copolyester was examined in the temperature range (T c ) from 30 to 80 C with the use of differential scanning calorimetry (DSC). The melting behavior after isothermal crystallization was studied with DSC by varying the T c , the heating rate, and the crystallization time. The complex melting behavior involves both mechanisms of various lamellar crystals and melting-recrystallization-remelting. As the T c increases, the contribution of recrystallization gradually decreases and finally disappears. The Hoffman-Weeks linear plot yielded an equilibrium melting temperature of 111.1 C, which is 1.6 C less than that of poly(ethylene succinate) (PES). The kinetic analysis of the spherulitic growth rates (G) indicated that a regime II!III transition occurred at $59 C (T II!III ), which is $ 11 C less than that of PES. The overall crystallization rate, T II!III and G indicate that the random incorporation of only 7.3 mol % BS units into PES significantly inhibits the crystallization rate of PES. Finally, the morphology of melt-crystallized samples was examined using polarized light microscopy and scanning electron microscopy.
Copolyester was synthesized and characterized as having 89.9 mol % ethylene succinate units and 10.1 mol % butylene succinate units in a random sequence, as revealed by NMR. Isothermal crystallization kinetics was studied in the temperature range (T c ) from 30 to 73 C using differential scanning calorimetry (DSC). The melting behavior after isothermal crystallization was investigated using DSC by varying the T c , the heating rate and the crystallization time. DSC curves showed triple melting peaks. The melting behavior indicates that the upper melting peaks are associated primarily with the melting of lamellar crystals with various stabilities. As the T c increases, the contribution of recrystallization slowly decreases and finally disappears. A Hoffman-Weeks linear plot gives an equilibrium melting temperature of 107.0 C. The spherulite growth of this copolyester from 80 to 20 C at a cooling rate of 2 or 4 C/min was monitored and recorded using an optical microscope equipped with a CCD camera. Continuous growth rates between melting and glass transition temperatures can be obtained after curve-fitting procedures. These data fit well with those data points measured in the isothermal experiments. These data were analyzed with the Hoffman and Lauritzen theory. A regime II ! III transition was detected at around 52 C.
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