We present an experimental technique for nondestructive measurement of the glass transition temperature (Tg) of thin nonlinear optical (NLO) polymer films by attenuated total reflection spectroscopy. At Tg the thermal expansion coefficient and temperature dependence of the refractive index ∂n/∂T change discontinuously. This change can be detected with high sensitivity by recording thickness and refractive index of a polymer waveguide coated on a glass/gold substrate as a function of temperature. Measurements were made on various high Tg NLO polymers (Tg up to 170 °C). The resulting Tg values are compared with those determined by differential scanning calorimetry of the bulk material.
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Böck et al. (1997) studied this question.
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