Abstract
The observation of multiple melting phenomena in poly(ethylene terephtha- late) (PET) by DSC or DTA has been confirmed to arise from recrystallization by the changes in birefringence occurring in the thermal regime of the polymer. Isothermal birefringence changes illustrate the melting of crystallites around 230–248 °C, with the formation of more perfect and higher melting crystallites at temperatures of annealing above 248°C. The formation of diethylene glycol residues in the PET during solid state polymerization may be a cause of the higher melting endotherm occurring at lower temperatures when annealed under vacuum.
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