Morphology of poly(ethylene naphthalene-2,6-dicarboxylate): First stages of crystallization

The morphology of poly(ethylene naphthalene-2,6-dicarboxylate) (PEN) with a wide range of crystallinities has been determined by transmission electron microscopy (TEM). PEN thin films undergoing cold crystallization during annealing at temperatures above T-g have been investigated after selective chemical staining and cutting in an ultramicrotome. Crystallization appears in amorphous areas distributed in a noncrystallizable matrix by formation of lamellae inside these amorphous areas. For low annealing temperatures (T-c similar to 145 degrees C), the emerging morphology of PEN is seen prior to the occurrence of crystallinity in the x-ray diffraction patten. With increasing time and temperature 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 finer with increasing crystallization time.