A poly(methyl methacrylate) (PMMA) glass was prepared for the first time, in which the light-scattering loss was much smaller than any reported data and no large size of heterogeneities existed. The total scattering loss was 13 dB/km which represents an intrinsic limiting loss of the PMMA glasses attainable in the atmosphere. The isotropic scattering loss widely varied between ca. 9 and 400 dB/km according to the conditions of polymerization or heat treatment, while the anisotropic scattering loss was almost unchanged in the range 4–6 dB/km. The origins of the large heterogeneities with the dimension of ca. 1000 Å, which have been invariably observed in PMMA glasses reported so far, were investigated by the angular dependence of the light scattering. The large excess scattering is caused mainly by the isotropic strain inhomogeneities caused during polymerization and not by a small amount of remaining monomers or additives, the molecular weight of polymers, the stereoregularity due to the specific tacticity of PMMA, or cross-linking as a result of the gel effect.
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