In the project, our purpose is the synthesis of segmented block copolymers using novel selectively reacting bi-functional coupling agents which have recently been developed by Jakisch at al. Both couplers have one oxazoline group that reacts with carboxylic groups and one oxazinone group that reacts with hydroxyl or amino groups. It was intended to synthesize segmented block copolymers by combination of amino or hydroxyl terminated pre-polymers and carboxylic terminated chain extenders using the above mentioned coupling agents. Several prepolymers were selected such as hydroxyl terminated liquid polybutadiene (PBD-OH), hydroxyl terminated liquid natural rubber (LNR) and amino terminated liquid polybutadiene-b-acrylonitrile (PBAN) and poly(propylene glycol)-bis(2-aminopropylether) (PPO). They were selected as soft polymer segments in the segmented block copolymers aimed for. Additionally, various di-carboxylic acids were chosen as chain extenders. The resulting block copolymers are phase separated materials with a crystalline hard phase. This was demonstrated by two glass transition temperatures corresponding to the soft and hard segments and various melting regions of the hard chain extenders. For these new materials, the controlled phase separation morphology in nano-size was evidenced by TEM. A hard domain size of about 2-5 nm surrounded by a soft matrix was observed on the micro-photographs. This is consistent with the low hard segment content and the segment alternation (A-B)n in multi-block copolymers. With respect to the mechanical properties, a relationship between tensile strength and the average molar mass of the block copolymers was found out. The samples behave as rubber-like thermoplastic materials. The tensile properties depend on the degree of polymerization and the polymer distribution. The reinforcement ability of the hard domains in a physical network was achieved as expected. As a consequence, the obtained final products have mechanical properties like a typical elastomeric material.