TOWARD CHAIN EXTENSION IN CRYSTALS OF FLUORINATED COPOLYMERS AS REVEALED BY REAL-TIME ULTRA-SMALL-ANGLE X-RAY-SCATTERING

We have measured with the ultra-small-angle scattering technique, USAX S, long periods of the order of 120-130 nm in fluorinated copolymers. These unusually large spacings were obtained when copolymers of vinyli dene fluoride and trifluoroethylene, with 60% and 80% molar content of vinylidene fluoride, were annealed near the melting point. The format ion of crystal stacks during annealing up to a long period of 120 nm w as followed in real time. The growth of structures giving rise to long periods of about 100 nm was also observed upon crystallization from t he melt. Annealing experiments performed in the hexagonal and in the o rthorhombic phases show that polymorphism plays an important role in t he thickening of the crystals in accordance with the predictions of th e Chain sliding diffusion theory.