When polymers are used in new areas of application or different materials are combined in an innovative way, it is the interfaces and their design that really matter. Block copolymers have proven to be a very versatile tool for this purpose and they are currently being developed by the Plastics Division of the Fraunhofer Institute for Structural Durability and System Reliability LBF. With the appropriate design, the block copolymers adsorb in the interface, thereby improving the property profile of the multiphase polymer systems. The Institute matches the blocks of the copolymers to the materials that need to be combined and designs customized solutions for a variety of different polymers. These include, for example, polyolefins or polycondensates in which the synthesis of block copolymers is very demanding. It is also possible to integrate suitable functional anchor groups in the compatibilizer for attaching polymers to surfaces of different classes of materials, such as inorganic and organic fillers and fibers, as well as glass, ceramic or metal surfaces. With block copolymers as adhesion and phase compatibilizers, the Fraunhofer LBF can improve the mechanical, physical or optical properties of various materials. For example, the Institute is currently optimizing thermoplastic elastomers, impact modification of brittle polymers, and also adhesion between polymers and materials of other classes.