Synthesis of Re-Processable Polyurea Thermosets from CO₂-Based Oligourea and Formaldehyde

The synthesis of functional polymer materials from CO2, an abundant and cheap feedstock, is of great significance from the viewpoint of green and sustainable development. Using CO2 as monomer to produce functional polymeric materials can reduce not only fossil consumption but also CO2 emissions. Herein, we designed a re-processable polyurea thermoset from formaldehyde and CO2-based oligourea, which is an amino-terminated oligomer derived from CO2 and 4,7,10-trioxa-1,13-tridecanediamine. The CO2-based oligourea reacted with formaldehyde to form polyurea hemiaminal networks (PHNs) with a hemiaminal structure and reversible hydrogen bonds. PHNs are of good mechanical properties due to their intermolecular hydrogen bonds and cross-linked structure. Moreover, the reversible non-covalent hydrogen bonds and hemiaminal structure in the chains enabled PHNs to be re-processable. The synthesized polyurea thermoset can be hot-molded, the tensile strength is about 20 MPa, and the elongation at break is about 20% of the original sample. In addition, the tensile strength and toughness can be nearly recovered after hot-reprocessed for 6 cycles. This is the first report of the re-processable thermosetting polyurea from CO2 designed by hydrogen bonds and hemiaminal cross-linking structure.