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.