Tetramethylene urea (TeU) is successfully copolymerized with gamma-butyrolactone (yBL), leading to an alternating poly(amide urethane) with alternating carbonyl-amino-tetramethylene-amino and carbonyl-trimethylene-oxy repeating units (M-n = 12 600; M-w = 21 100; M-n = 1.67) and with a T-m of 196.5 degreesC and a T-g of 36.4 degreesC. Small defects in the microstructure of the alternating poly(amide urethane) arise from the formation of TeU-TeU diads. Furthermore, TeU is successfully copolymerized with mixtures of gammaBL and ethylene carbonate (EC) or 1,2-propylene carbonate (PC). From NMR spectroscopic data of the terpolymers obtained, it is concluded that the reactivity of the five-membered cycles used increases in the following order: EC much greater than PC approximate to gammaBL. It is possible to increase the content of gammaBL repeating units in the poly[(TeU-gammaBL)-stat-(TeU-EC)] or poly[(TeU-gammaBL)-stat-(TeU-PC)] by increasing the fraction of gammaBL in the feed. C-13 NMR spectroscopy reveals that TeU-EC or TeU-PC and TeU-gammaBL units are randomly distributed in the polymer chain. This conclusion is supported by the thermal properties.