The preparation of copolyester from dimethyl terephthalate (DMT), ethylene glycol (EG) and 1,4-butanediol(BD) by melt polycondensation process and its solid state polycondensation process has been studied The compositions of copolyester have been determined by NMR spectroscopy. In the melt polycondensation process, the glass transition temperature(Tg) and melting temperature(Tm) was decreased with the increase of BD contents of copolyester. In the solid state polycondensation, the reaction rate was found to be dependent on the reaction time, temperature and BD contents of copolyester. Increasing reaction rates, the contents of carboxyl end groups are decreased. By the solid state polycondensation double melting endotherm peaks are appeared and discussed. The change of crystal structure was not observed during the solid state polycondensation but the crystallinities are increased with the increase of reaction rate.

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