Certain natural materials such as bones not only show high stiffness and high damping performance but also exhibit other superior properties as the result of complex hierarchical structure formation. Synthetic polymer materials have demonstrated a great versatility to mimic certain features of biomaterials, achieve hierarchical structures on different lengths scales, and access a wide range of property profiles by making use of competing molecular interactions. In this context, the current thesis explored the hierarchical structure formation and mechanical properties of oligopeptide-modified polymer materials in order to achieve an unusual combination of high stiffness and high damping performance. To this end, we investigated the co-assembly of oligopeptide-modified poly(isobutylene) and poly(styrene) with an identical number of amino acid residues in the oligopeptide segments, driven by the competition between hydrogen-bond-driven aggregation of the oligopeptide segments and phase segregation of polymer segments. The obtained polymer blends were systematically compared to the mixtures of oligopeptide-modified poly(isobutylene) and unmodified poly(styrene). The properties of both series of binary blends, such as the secondary structure formation in organic solvents and in the solid state, thermal properties, morphologies, as well as rheological properties were investigated. Phase segregation on smaller scale and higher stiffness were observed in the case of the blends with oligopeptide-modified poly(styrene). Based on the investigation of these binary blends, the best candidates were then used as reinforcing and structure-directing additives in poly(isobutylene)-based materials. Further addition of poly(styrene) microbeads as a filler to these ternary blend finally gave rise to materials with high stiffness and high damping performance in constrained layer damping applications.