Isothermal aging has been carried out on low-loss poly(methyl methacrylate) (PMMA) glass at 18°C below the glass transition temperature (Tg). The effect of enthalpy relaxation on light scattering loss of PMMA glass which had no excess scattering was investigated by the use of differential scanning calorimeter (DSC) and light scattering measurement. The light scattering intensity of PMMA glass did not increase with increasing aging time. It is seen that the light scattering loss of glassy PMMA is not affected inherently by physical aging as a result of its approach to thermodynamic equilibrium at a temperature 18°C below its Tg.
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