Communication: The protection of solar energy collecting technology against overheating can be achieved using the co-polymer reported here. In the form of a semi-interpenetrating polymer network, the co-polymer demixes when the temperature rises above a certain value (which can be tuned between 30 and 150 degrees C by adjusting the ratio of the repeat units of the components). In the phase-separated state the light transmission of the material is reduced significantly by backward light scattering.