Determination of the crosslinking temperature of the thermally crosslinkable polyurethane by attenuated total reflection spectrum

An experimental technique is presented in this paper for the measurement of the crosslinking temperature (Tcrosslinking) of the polymer films by using the attenuated total reflection (ATR) spectrum. According to the change of the ATR spectrum, the changing value of the refractive index of the polymer film can be determined during the ascending temperature. Experimental results definitely show that the temperature dependence of the refractive index dn/dT changes discontinuously. By linear fits, the dn/dT curve exists two intersection points. The temperature range between two intersection points is regarded as Tcrosslinking. The crosslinking range of the polyurethane is determined as the range from 85 °C to 122 °C. It is examined and convinced by the measurement of electro-optic r33 coefficient of the poled polyurethane film with several temperatures in the range of Tcrosslinking at which poling is started.