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

Abstract 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 Tg 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 (Tc ∼ 145°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.