Segmented block copolymers, consisting of non-polar soft segments from hydroxyl-terminated liquid natural rubber (HTNR) and polar hard segments from alpha,omega-diisocyanato telechelics obtained by "criss-cross"-cycloaddition, have been synthesized. The block copolymer formation took place under relatively mild reaction conditions at 80 T in dichloroethane in the presence of dibutyltin dilaurate as a catalyst. The resulting block copolymers were characterized by spectroscopic techniques (H-1 NMR, FTIR, UV-vis spectroscopy) as well as GPC for molar mass determination. The block copolymers were compression molded in a hot stage press, and the resulting samples were characterized by DSC and stress-strain measurement. The solubility and phase morphology of the materials have also been studied.