Abstract: Aseries of copolyesters poly(ethylene terephthalate p-oxybenzoate) (PETO) de-rived from terephthalic acid, ethylene glycol and 4, 4' -oxybis (benzoic acid) were easily pre-pared by using DMT method and thermally investigated.Introduction of 4, 4' -oxydipheny-lene group into the main chain resulted in a lowering of T_{m.a decrease of crystallization rate and an increase of thermal-oxidative stability of the copolyesters.By static elongation of PETO, transparent films with qualified electrical properties and mechanical properties were easily obtained with film forming rate 100%.In comparison with poly (ethylene terephthalate) (PET) film, PETOfilm had obviously low Tm.and low crystallization temper-ature.Due to the presence of stable aromatic ether structure, decrease in Tm.could not lead to any reduction in thermal-oxidative stability, on the contrary, slight increase was ob-served.PETOfilm could be used in making heat resistant thick film for channel insulators of electric motor.}

Key words: Poly (ethylene terephthalate p-oxybenzoate), 4,4' -Oxybis (benzoic acid), Electric insulating film