STRUCTURES OF POLY(ETHYLENE/BUTYLENE TEREPHTHALATE) COPOLYESTERS UNDER ISOTHERMAL CRYSTALLIZATION CONDITIONS

In this experiment, poly(ethylene/butylene terephthalate) (EB) copolyesters were synthesized from ethylene glycol (EG), 1,4-butanediol (BDO), and dimethyl terephthalate with different molar volume ratios. The structure of EB copolyesters under isothermal crystallization conditions were investigated using a wide-angle X-ray diffraction (WARD), a small-angle X-ray scattering (SAXS), and a differential scanning calorimetry (DSC). Compared with the non-isothermal crystallization of EB copolyesters, the WAXD deconvolution results showed EB copolyesters have more diffraction peaks formed under isothermal crystallization conditions. The thicknesses of long period (L) and crystalline layer (l(c)) were determined from correlation function analysis of the SAXS data. The crystalline layer thickness decreased obviously at the PET-rich copolyesters. The linear crystallinity decreased with increasing the minor co-monomer content. In addition, multiple melting behaviors in DSC heating trace were found. The lowest melting point temperature occurred in EB70 (EG/BDO: 50.1/49.9). However, the minimum values of crystalline layer, linear crystallinity and melting enthalpy occurred in EB80 (EG/BDO : 65.7/34.3).