STUDY ON THE PREPARATION AND STRUCTURE PROPERTIES OF PETG COPOLYESTERS

摘要

Copolyesters Poly(ethylene terephthalate-co-1,4-cylclohexylenedimethylene terephthalate)(PETG) were synthesized from dimethyl terephthalate(DMT), ethylene glycol(EG) and 1,4-cyclohexanedimethanol(CHDM) in various molar ratio by melt polycondensation. The optimum condition for PETG copolyester preparation was the transesterification at a temperature of 170 to 210°C, followed by polymerization at a temperature of 260 to 300°C in the presence of composite catalysts. The thermal and crystalline properties of the resulted copolyesters were investigated using the differential scanning calorimetry (DSC) and the wide angle x-ray diffraction (WAXD). The comonomer contents (ET/CT) in coploesters were determined by 1{sup left}H nuclear magnetic resonance (1{sup left}H-NMR). The experimental results indicated that the glass transition temperature (Tg) of PETG copolyesters increased with an increase in CHDM content. From the 1{sup left}H-NMR results it was also found that the actual ratios of ET/CT in the copolyesters were different from the feed ratios of EG/CHDM. When the comonomer contents EG/CHDM in the feed were 80/20 and 75/25, the actual molar ratios of ET/CT in the gained copolymer PETG were 70/30 and 48/52 respectively and the corresponding PETG copolyesters were amorphous, that was, they had neither Tc nor Tm. The WAXD results showed that the crystallinity of the coplolymers changed with the CHDM content in the polymers.