Recyclable and Degradable Vinylogous Urethane Epoxy Thermosets with Tunable Mechanical Properties from Isosorbide and Vanillic Acid

Conventional epoxy resins derived from unsustainable petroleum resources are unrecyclable and nondegradable. Herein, we facilely synthesized biobased vinylogous urethane epoxy thermosets (VUEs) using sustainable isosorbide and vanillic acid via a post-crosslinking method. Isosorbide was directly functionalized to isosorbide-bis-acetoacetate, which could be reacted with primary amines provided by triethylenetetramine and diamine to generate linear prepolymers with vinylogous urethane bonds. Then, VUEs were constructed, in which permanent covalent crosslinkers were generated by ring opening of the epoxy group in vanillin acid with the secondary amine already present in the linear prepolymer. By integrating different types of diamines, the obtained biobased VUEs display tunable mechanical properties; specifically, the tensile strength varies from 31.5 to 114.6 MPa and the elongation at break ranges from 9.5 to 150.0%. The VUE using ethylenediamine (TT-VUE) is comparable to that of bisphenol-A epoxy in terms of its mechanical qualities. The incorporation of vinylogous urethane bonds confers recyclable capability on VUEs, and the recycled VUEs show a lap shear strength of 7.39 MPa, indicating their potential application in adhesives. We envisaged that biobased VUEs with desirable tunable mechanical properties would be excellent replacements for petroleum-based epoxy resins.