Thermoplastic and Reprocessable Polyureas Synthesized from CO2-Based Oligourea

Abstract

Polyureas (PUas) are a versatile class of polymers with wide applications in coatings, flexible electronics, 3D printing, and engineering protection. Herein, a series of thermoplastic PUas with diverse properties were prepared from diisocyanates with different structures and a carbon-dioxide-based oligourea (OUa). First, OUa was synthesized from diamines and carbon dioxide (CO₂); then a group of thermoplastic PUas were fabricated by reacting OUa with diisocyanates. The formation of CO₂-based OUa and its subsequent polymerization with diisocyanates are necessary steps in producing high-performance PUas. The properties of the synthesized PUas depend on the diisocyanate structure. While 4,4′-diphenylmethane diisocyanate (MDI) and CO₂-based OUa produced a tough material with excellent mechanical properties including a tensile strength of 62 MPa, Young’s modulus of 1104 MPa, elongation at break of 209%, and toughness of 85 MJ·m^–3, 1,6-hexamethylene diisocyanate (HDI) and CO₂-based OUa produced an elastic material with a tensile strength of 50.5 MPa, Young’s modulus of 382 MPa, elongation at break of 456%, and toughness of 129 MJ·m^–3. Moreover, PUa derived from HDI and OUa also presented excellent damping properties with an energy absorption efficiency of 94% and an energy dissipation density of 23.0 MJ·m^–3. It could be used as a damping and protective material for wheels, buildings, driveways, etc. It is worth noting that the PUas also exhibited good reprocessing properties, maintaining their mechanical properties after two cycles of reprocessing. Additionally, all the PUas showed good thermal stability, with initial degradation temperature values ranging from 287 to 313 °C.