The morphology of poly(ethylene naphthalene-2,6-dicarboxylate) (PEN) w
ith a wide range of crystallinities has been determined by transmissio
n electron microscopy (TEM). PEN thin films undergoing cold crystalliz
ation during annealing at temperatures above T-g have been investigate
d after selective chemical staining and cutting in an ultramicrotome.
Crystallization appears in amorphous areas distributed in a noncrystal
lizable matrix by formation of lamellae inside these amorphous areas.
For low annealing temperatures (T-c similar to 145 degrees C), the eme
rging morphology of PEN is seen prior to the occurrence of crystallini
ty in the x-ray diffraction patten. With increasing time and temperatu
re of crystallization, the number and thickness of lamellae increase,
in accordance with increasing crystallinity and crystalline thickness,
as determined by x-ray investigations. Dendritic superstructures are
also observed with a rough starting internal structure that becomes fi
ner with increasing crystallization time.