The conversion of 1,3-bis-(6-amino-pyridin-2-yl)-urea (1) with N,N'-carbonyldiimidazole at high temperatures in DMSO yielded a mixture of defined cyclic trimers and tetramers. On the basis of model reactions, exchange reactions were evidenced, which convert the cyclic tetramer into a stable cyclic trimer. Linear even numbered oligomers were obtained in acetone under reflux where side reactions were suppressed. The pronounced tendency of cyclization is attributed to a preferred folded conformation of the urea bond between two pyridyl units.

A series of alternating polyester/polyamide block copolymers were prepared by sequential conversion of hydroxy-terminated polycaprolactone and amino-terminated polyamide-12 with a selectively reacting coupling agent. The thermal properties of the block copolymers were investigated using differential scanning calorimetry and dynamic mechanical analysis. Mechanical properties were determined using tensile and impact tests. All polymers were phase-separated, where the polyamide phase was semicrystalline in all compositions. Distinct crystallization of the polycaprolactone phase was observed only when the block length was greater than 2000 g mol −1 . Mechanical testing showed that the polymers behave in a manner similar to that of thermoplastic elastomers. In particular, samples with a high content of polycaprolactone showed high strain and good impact behaviour.