A reaction of aziridines and carbon dioxide (CO2) proceeds under supercritical conditions to give random copolymers containing urethane and amine moieties. The ratio of urethane and amine linkages in the product can be controlled by reaction conditions including temperature and pressure as well as addition of NN-dimethylacetamide as a cosolvent. An aqueous solution of the copolymer obtained from 2-methylaziridine and CO2 undergoes a thermally induced phase transition at a lower critical solution temperature (LCST). The critical temperature is highly sensitive to changes in the primary structure of the products. The use of supercritical CO2 (scCO(2)) allows us to construct a functional material through the effective chemical fixation of CO2.