Design of Isocyanate-Free Biobased Polyurea Vitrimers with Dynamic Hydrogen and Imine Bonds, Offering Ambient Self-Healing, Reprocessing, and Recycling Properties

A series of vitrimers combining dynamic hydrogen and imine bonds was prepared by a reaction between amine-terminated nonisocyanate polyurea oligomers (NIPUrea), terephthalaldehyde, and tris(2-aminoethyl)amine at various equivalent ratios. NIPUrea oligomers of different molecular weights were prepared using an environmentally friendly and sustainable approach, implying transurethane polycondensation technology. The vitrimers prepared possessed different cross-linking densities and exhibited T_g values of around 20 °C, as well as thermal stabilities exceeding 300 °C. They displayed high and tunable mechanical strength and ductility, with Young’s modulus from 1.7 to 26.4 MPa, breaking stress from 7.9 to 12.9 MPa and elongation at break from 147 to 517%. They revealed good solvent resistance except in acidic THF/water solutions, in which they underwent irreversible degradation and solubilization. Most of the materials prepared exhibited excellent self-healing efficiency at room temperature (93 to 107%) and good reprocessability and recyclability after hot pressing.