Copolymerization of equimolar amounts of 2,2-dimethyltrimethylene carbonate (DTC) with tetramethylene urea (TeU) results in a copolymer the microstructure of which depends on the reaction conditions and on the catalyst used. With sec-butyllithium, dibutylmagnesium and diethylzinc as a catalyst a nearly alternating copolymer, i.e. a polyurethane, was obtained. With dibutyldimethoxytin, tris(sec-butoxyaluminium), and tetrakis(iso-propoxytitanium) as a catalyst copolymers with carbonate, urea, and urethane groups were obtained.