Poly(butylene succinate) (PBSu) and two PBSu-rich poly(butylene succinate-co-propylene succinate)s were studied. Copolyesters were characterized as random copolymers, based on 13 C-NMR spectra. TGA-FTIR was used to monitor the degradation products at a heating rate of 5 C/min under N 2 . FTIR spectra revealed that the major products were anhydrides, which were formed following two cyclic intramolecular degradation mechanisms by the breaking of the weak O-CH 2 bonds around succinate groups. Thermal stability at heating rates of 1, 3, 5, and 10 C/min under N 2 was investigated using TGA. The model-free methods of the Friedman and Ozawa equations are useful for studying the activation energy of degradation in each period of mass loss. The results reveal that the random incorporation of minor propylene succinate units into PBSu did not markedly affect their thermal resistance. Two model-fitting mechanisms were used to determine the mass loss function f(a), the activation energy and the associated mechanism. The mechanism of autocatalysis nth-order, with f(a) ¼ a m (1 À a) n , fitted the experimental data much more closely than did the nth-order mechanism given by f(a) ¼ (1 À a) n . The obtained activation energy was used to estimate the failure temperature (T f ). The values of T f for a mass loss of 5% and an endurance time of 60,000 h are 160.7, 155.5, and 159.3 C for PBSu and two the copolyesters, respectively.

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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Poly(butylene succinate) (PBSu) and two poly(butylene succinate‐co‐propylene succinate)s were synthesized via the direct polycondensation reaction. The copolyesters were characterized as having 7.0.and 11.5 mol % propylene succinate (PS) units, respectively, by 1H NMR. A differential scanning calorimeter (DSC) and a polarized light microscope (PLM) adopted to study the nonisothermal crystallization of these polyesters at a cooling rate of 1, 2, 3, 5, 6, and 10 °C/min. Morphology and the isothermal growth rates of spherulites under PLM experiments were monitored and obtained by curve‐fitting. These continuous rate data were analyzed with the Lauritzen−Hoffman equation. A transition of regime II → III was found at 95.6, 84.4, and 77.3 °C for PBSu, PBPSu 95/5, and PBPSu 90/10, respectively. DSC exothermic curves show that all of the nonisothermal crystallization occurred in regime III. DSC data were analyzed using modified Avrami, Ozawa, Mo, Friedman, and Vyazovkin equations. All the results of PLM and DSC measurements indicate that incorporation of minor PS units into PBSu markedly inhibits the crystallization of the resulting polymer. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1299–1308, 2010