Catalyst-Free, High-Strength, Reprocessable, and Closed-Loop Recycling Biobased Poly(β-Hydroxyurethane) Vitrimers with Vinylogous Urethane Segments

Biobased poly(β-hydroxyurethane) (PHU) vitrimers, as one important kind of nonisocyanate polyurethanes, have attracted widespread attention due to their remarkable benefits for sustainable development and green production. However, the balance between good mechanical properties and high reprocessing efficiency has not been well resolved, which affects their large-scale production and practical applications as substitutes for conventional isocyanate polyurethanes. In this study, a series of biobased PHU vitrimers (PDGVU6s) with vinylogous urethane (VU) bonds were prepared through a one-pot polymerization of a diglycerol dicyclic carbonate (DGDC) and a diglycerol tetraacetoacetate (DGTAA) with hexamethylenediamine (HDA). Thereinto, DGTAA was designed as a cross-linking agent to react with amino groups and form VU dynamic covalent bonds. Appropriate DGDC/DGTAA ratios and the incorporation of VU dynamic bonds enabled PDGVU6s to show good performance. The tensile strength of PDGVU6 films was high, up to 53.4 MPa. They exhibited relaxation activation energy from 36.55 to 97.52 kJ/mol, good third reprocessing efficiency up to 91.6%, good self-healing, shape-memory property, and closed-loop recycling. Moreover, the abundant polar bonds in PDGVU6s endowed them with good adhesive properties, achieving a maximum bonding strength of 7.39 MPa at room temperature. This novel biobased PHU vitrimers demonstrate outstanding advantages including superior mechanical properties, thermal stability, and closed-loop recycling property. This study establishes a sustainable pathway to the development of PHU vitrimers.