Segmented block copolymers were synthesized in melt by conversion of carboxy-terminated poly(propylene oxide) and amino-terminated PA12 with a selectively reacting bifunctional coupling agent bearing one oxazoline and one oxazinone group. The reaction was performed either in one or two steps. In the latter, it could be shown that the sequence of mixing significantly influenced the course of reaction. The structure of the linking group formed (luring the reaction was verified by H-1 NMR spectroscopy using model compounds. DSC and TEM investigations evidenced that the block copolymers are phase separated. Domains in a size of several nanometers are found. Owing to the two phase structure, the block copolymers show ductile behavior with the tendency to elastomeric behavior. Tensile properties of the block copolymers increase with the content of PA12. Elongations at break were measured with values up to 500%.