Temperature dependence of light scattering by low-loss poly(methyl methacrylate) glasses

A poly(methyl methacrylate) glass with the lowest light scattering loss (13 dB km⁻¹ at 633 nm wavelength) among data reported so far and with no angular dependence in its scattering intensity was prepared by radical polymerization above the glass transition temperature (Tg) (Sample A). The temperature dependence of the light scattering intensity for this PMMA glass was investigated, in comparison with the PMMA glass polymerized below Tg and having excess scattering loss (hundreds dB km⁻¹) due to large-size heterogeneous structures (Sample B). In the sample A, the polarized scattering intensity (VV) slightly changed below Tg and increased smoothly with increasing temperature above Tg in accordance with the fluctuation theory for structureless liquids. On the other hand, in the sample B, an abrupt decrease in VV scattering around Tg was observed with increasing temperature. On the basis also of our previous study, it is suggested that the different trend of temperature dependences of light scattering and of excess scattering even in highly purified PMMA glasses depends on whether the strain inhomogeneities generated during the polymerization process are already relaxed above Tg or retained below Tg, and that the scattering behavior is not directly affected by first order structures such as molecular weight, tacticity, and remaining monomers.