Synthesis and characterization of amorphous poly(ethylene terephthalate) copolymers containing bis[4-(2-hydroxyethoxy)phenyl]sulfone

Poly(ethylene terephthalate) copolymers (abbreviated as PETS) that contain bis[4-(2-hydroxyethoxy)phenyl]sulfone (BHEPS) were prepared from dimethyl terephthalate (DMT), ethylene glycol (EG) (5–95%) and BHEPS (5–95%). The compositions and microstructures of the copolyesters were determined by 1H and 13C nuclear magnetic resonance (NMR) spectroscopy, respectively. The thermal behaviors were studied over the entire range of copolymer compositions, using X-ray analysis, differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA). The molecular weights, optical characteristics and tensile properties of these polymers were also determined. Experimental results indicated that the copolymers had a random microstructure. The intrinsic viscosities of the copolymers ranged from 0.65 to 0.69 dL/g. The copolyesters with BHEPS of <10 mol% were crystallizable, whereas the copolyesters with BHEPS of ⩾10 mol% were amorphous. Incorporating BHEPS affected the glass-transition temperature (Tg) values of those polymers, from about 81 °C for PETS5 to 126 °C for PETS95. The optical transmissions exceeded 86% for λ = 400 nm for all of the amorphous polyesters. The tensile modulus and strength of the copolyesters increased with BHEPS. However, they also became brittle and their elongation at break decreased.