Lifetime spectra of positron annihilation in amorphous and semicrystalline polyethylene terephthalate (PET) have been measured in the temperature range from 21 to 150℃. The lifetime data were analysed in terms of a three component fit. A sudden change of slope in the longest lifetime τ3 against temperature was found at 70℃ for amorphous and semi-crystalline PET respectively. The transition temperature obtained by this technique

so-called Ts

is insensitive to crystallinity of the sample. In general

the relative intensity of the longest lifetime component I3 increses with increasing temperature. However

due to the crystalliza-tion of amorphous sample the gradual decrease of I3 with increasing temperature between 100 and 110℃ was observed. Thus

the value of I3 is sensitive to variation of crystallinity of PET.