Dynamic Mechanical Properties of Poly(ethylene terephthalate)/Poly(ethylene 2,6-naphthalate) Blends

Blends of poly(ethylene terephthalate) (PET) and poly(ethylene 2,6-naphthalate) (PEN) with various compositions were prepared using a mixer at 290 °C and 100 rpm for various times. The transesterification level fTEN and the average chain lengths LPET and LPEN were determined using 1H NMR. The dynamic mechanical properties of PET/PEN blends were studied as functions of blend composition and transesterification level. This technique was found to be sufficiently sensitive to observe the change in the physical state and the molecular motions of PET/PEN blends in the glass transition and the subsequent cold-crystallization regions. For the PET/PEN blends having fTEN of above 10%, all the blends quenched from molten state exhibited the same dynamic mechanical behavior in the glass transition region showing a single glass transition temperature Tg. Tg of the blend was a linear function of the blend composition and independent of fTEN. For the PET/PEN blends having fTEN of about 5%, PET/PEN = 75/25 and 25/75 blen...