Determination of ultra-low glass transition temperature via differential scanning calorimetry

A novel method was developed to determine the ultra-low glass transition temperature (Tg) of materials through physical blending via differential scanning calorimetry. According to the Fox equation for polymer blends, a blend of two fully compatible polymers has only one Tg. The single Tg is a function of the Tgs of the two simple polymers. Thus, the ultra-low Tg of one material can be obtained from the Tgs of another polymer and their blends. The error of Tg measurements depends on the measurement error of the Tgs for the blends and another polymer. The method was successfully applied to determine the Tgs of acetyl tributyl citrate (ATBC), tributyl citrate (TBC) and poly(ethylene glycol)s (PEG)s with different molecular weights. The Tgs for ATBC, TBC, PEG-4000 and PEG-800 were −57.0 °C, −62.7 °C, −76.6 °C and −83.1 °C, respectively. For all the samples, the standard deviation of measurements was less than 3.3 °C, and the absolute error of measurements was theoretically not more than 5.3 °C. These results indicate that this method has acceptable precision and accuracy.