Cyclic oligourea synthesized from CO2: Purification, characterization and properties

Carbon dioxide (CO2) as a sustainable resource instead of toxic reagents has attracted considerable attention in synthesis of chemicals and polymeric materials. Herein, a kind of cyclic oligourea was synthesized via polycondensation of CO2 with 4,7,10-trioxa-1,13-tridecanediamine (TTD) followed by effective separation and purification processes. We developed an efficient separation strategy in which the linear oligourea molecules were selectively transformed to macromolecular polyurea molecules by a reaction of the –NH2 end group with 4,4′-diphenylmethane diisocyanate (MDI), followed by separation from cyclic oligourea using selected solvents. The structure and physicochemical properties were confirmed by MALDI-TOF mass spectra, NMR, Cryo-EM, thermal analysis and solubility measurement. The well-defined cyclic oligourea was produced with a high purity (99.4%) and the average-number molecular weight (Mn) of 1040 Da. It is semi-crystalline in structure with a melting point of 106 °C and glass transition point of −10 °C. The cyclic oligourea presented characteristically difference to its linear analogue. This work provides a new member to cyclic polymer family.