Toward chain extension in crystals of fluorinated copolymers as revealed by real time ultra-small-angle X-ray scattering

Abstract

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