The curve on the left shows some MT-DSC data for a sample of polystyrene (PS) sheet that was believed to be contaminated with some low molecular weight poly(alpha-methyl styrene) (PaMS). The step in heat capacity around 100°C corresponds to the glass transtion of PS and there is a small bump in the curve that was thought to be the response of the PaMS. The sample was investigated further by micro-TA. A region of in homogeneity was identified in the thermal image below across an interface between what appears to be two thermally dissimilar materials (bottom right). Localised TMA measurements on the top and bottom regions suggest that they are indeed different materials. The Tg's correspond to the features in the bulk MT-DSC results and indicate that the top area is PaMS and the bottom area is PS.

Following the TMA measurements, the thermal probe was used to pyrolyse the surface at the same locations. The GC-MS data detected difference in the evolved gases - the mass spectra of the main peaks form the GC-MS traces are shown below. These confirm that the top region is PaMS (by detecting alpha-methyl styrene) and the bottom region is PS (by detecting styrene).