Thermal behavior and cyclic oligomer composition of poly(ethylene terephthalate) copolymers

Thermal behavior and cyclic oligomer composition of poly(ethylene terephthalate) (PET) copolyesters obtained by introducing comonomers such as 1,4-cyclohexane dimethanol, neopentyl glycol, xylylene glycol, or 1,6-hexanediol as a diol and 2,6-dimethyl naphthalate as a diacid ester residue were analyzed. Ester interchange reaction rate between diol and 1,4-dimethyl terephthalate (DMT) depended on the diol and catalyst type. The activation energies for the thermal degradation of all copolyesters were similar to or higher than that of PET. From the results of experiment and theoretical calculation, the content of individual PET cyclic oligomer in PET copolyesters decreased with the increase of comonomer unit and more dramatically decreased with the increase of the repeating unit of cyclic oligomer, regardless of copolymer type. Cyclic trimer (C3) component of copolyester having 20 mole% comonomeric unit was decreased to half.