Molecular orientation in plastic optical fibres

Abstract

Molecular orientation in polystyrene fibres has been studied using polarized Fourier transform infrared spectroscopy. Polymerization of the monomers was carefully controlled to work with the same molecular weight and heterogeneity index. During drawing, the velocity of the fibres was maintained constant and the temperature was varied from 166 to 200 degrees C. Samples were cut from the different fibres. Two polarized spectra, with electric vectors parallel and perpendicular to the drawing direction, were recorded. The molecular orientation function was calculated from the area of the 1028 cm-1 peaks, which corresponds to the nu 18a in-plane CH bending normal mode of the aromatic ring. Results indicate that the molecular orientation depends strongly upon the drawing conditions. Annealing the fibre at a temperature slightly higher than the glass transition temperature allows one to recover most of the isotropic properties.