Polyurethane (PUR) elastomers based on Naphthalene-l,5-diisocyanate (NDI) are outstanding for their high performance in particularly demanding dynamic applications. For a better explanation and an understanding of their properties, suitable model systems for the technically relevant NDI-elastomers in the form of molecularly uniform oligourethanes and PUR-elastomers with uniform hard segments were synthesized and characterized. Detailed investigations of the microphase separation, the melting behavior, the thermal stability the hydrogen bonding behavior and the mechanical properties showed that the hard segment, built by the naphthalene bisurethane units with their rigid structure and their high melting points were responsible for the unusual material properties.