Syntheses and characterization of poly(ethylene terephthalate) modified with p-acetoxybenzoic acid

Though the structure and properties of a copolyester of 40 mole % of polyet hylene terephthalate (PET) and 60 mole % p-hydroxybenzoic acid (PHB) (PET/6 0PHB) and their blends have been well documented, no work has been reported in an open literature on the systematic investigation of the PET copolymer s modified with broad range of p-acetoxybenzoic acid (PABA) composition as yet. In this study, several PETA-x copolyesters having various PAPA composi tions from 10 to 70 mole % were prepared by the melt reaction of PABA and P ET without a catalyst, where x denotes the mole % of PAPA. And the modified polyesters obtained were characterized by H-1-NMR spectrophotometry, X-ray diffraction pattern, polarizing microscopy, thermal analysis, and rheometr y. The anisotropic phase appeared when x is above 50 mole % of PABA, and es pecially for the x's of 60 and 70 mole %, the nematic liquid crystalline te xture appeared clearly on the whole matrix. As the mole % of PAPA increased , melting temperature, heat of fusion, crystalline temperature, degree of c rystallinity, and the glass transition temperature of the modified PET were decreased, but the thermal stabilities of those copolyesters were increase d. The dependence of melt viscosity on the shear rate for PETA-50 similar t o 70 followed the typical rheological behavior of liquid crystalline polyme rs. Finally, it was concluded that the PETA-x copolyesters having compositi ons of higher than 50 mole % of PAPA exhibit the behavior of thermotropic l iquid crystalline polymers. (C) 1999 John Wiley & Sons, Inc.