Characterizing the microscopic dynamics of polymer films and coatings is a very important step in every new development or quality control, especially at high temperature. We use dynamic light scattering in the highly multiple scattering regime (Diffusing Wave Spectroscopy, DWS) to investigate the microscopic dynamics evolution at constant or increasing temperature (RT-250°C) and to detect the phase transition temperature (Tg) for different films with a very easy sampling protocol and a very high sensitivity. We propose a new, non-invasive, very sensitive and cost-effective method. Several examples show the influence of the temperature on the drying, the evaporation before curing, the curing and the phase transition, which will allow the optimization of materials development providing new insights.