Copolymerization of tetramethylene urea (TeU, 1) with the cyclic carbonates 2,2-dimethyltrimethylene carbonate (DTC, 2) and ethylene carbonate (EC, 3) results in the polyurethanes 4 and 5 with an approximate number-average molecular weight of 20000 and a polydispersity index of two. Polyurethane 4 is an amorphous material with a glass transition temperature of 26.3 degrees C; polyurethane 5 is a semicrystalline material with a melting temperature of 208 degrees C. Distinct copolymerization mechanisms are proposed for the formation of polyurethane 4 and 5, respectively.