Light Scattering and Local Structure in Low-Loss Poly(methyl methacrylate) Glasses

The attenuation of light transmittance through a plastic optical fiber in the range of visible light is governed by light scattering loss. In this paper, the possibility of decreasing scattering loss in poly(methyl methacrylate) (PMMA), which is one of the core materials of a plastic optical fiber, is discussed. The light scattering loss of the PMMA glass prepared from a contaminant-free monomer depended on the conditions of polymerization and heat-treatment. We succeeded in preparing the PMMA glass with a light scattering loss lower than the value, 14 dB/km, which was reported as the theoretical limitation at 633 (nm)-wavelenght in the fluctuation theory for structureless liquids. The angular dependence of light-scattering intensity suggested the existence of heterogeneous regions (several hundreds Å) with the order of 10⁻⁵ of refractive-index differences. This fluctuation would be caused by the stress-strain due to volume-contraction during polymerization or by the aggregation of polymer with a high molecular weight, but not by the inherent tacticity nor by the small amount of remaining monomer.