Series of polyurethaneurea elastomers were prepared from 4,4’-diphenylmethane diisocyanate, poly (tetramethylene ether) glycol and poly (hexamethylene carbonate) glycol for mixed soft segments, and 1,4-butanediol and isophoronediamine for mixed chain extenders. Characteristics of the copolymers related with compositions were examined. FT-IR spectra showed that most of the urea carbonyl groups associated in hydrogen bonding, while urethane carbonyls only partially did so. Thermal and mechanical properties were investigated through differential scanning calorimetry and tensile testing. These thermal and mechanical properties are discussed from the viewpoint of microphase domain separation of hard and soft segments.