Higher traffic volume and axle loads (EC-Regulations) require better pavement structures. To meet this requirements our company has developed a method for modifying bitumen with polymers, especially with polyolefins. In the past we made the experience that we do not need necessarily virgin material as a modifying agent, but we can also use-recycled polyolefins. But we also discovered that not every polyolefins material is compatible with every bitumen. To improve the properties of our modified bitumen it is necessary to know more about the chemical and physical reactions taking place between bitumen and polyolefin material. It seems that this reactions affect in an important way the physical behaviour of the polymer modified bitumen. This knowledge will allow us in the future to develop a modified bitumen, which will better meet the required climatic and physical properties with local raw materials available on every construction site.