The glass transition temperature of polymers depends on both the experimental procedures and the experimental techniques used for its evaluation. However, the value of the published data is often diminished because these details are omitted. Examples are cited to show how the magnitude of differential scanning calorimetry (DSC) Tg depends on the Tg location and different calibration methods. Some comments are also made about thermomechanical analysis (TMA) and dynamic mechanical analysis (DMA) methods, although these are treated only briefly.
The factors that are unique to elastomer glass transition temperatures are: (1) the difficulties of calibration of the instruments at subambient temperature, (2) increase of Tg by the extent of vulcanization and filler loading, (3) differences due to microstructure and microphase separation, and (4) the availability of different grades of the same elastomer with different composition or added components, which alter their Tg. Thus, the literature value of Tg should include not only the calibration and procedure for the experiment, but also the exact name and description of the elastomer with the number index, the recipe used, and the cure conditions.