Lignin-derivable alternatives to petroleum-derived non-isocyanate polyurethane thermosets with enhanced toughness

The structural similarities between lignin-derivable bisguaiacols and petroleum-derived bisphenol A/F (BPA/BPF) suggest that bisguaiacols could be ideal biobased alternatives to BPA/BPF in non-isocyanate polyurethane (NIPU) thermosets. Herein, bisguaiacol/bisphenol-derived cyclic carbonates with variations in methoxy content and bridging-carbon substitution were cured with two triamines of different chain lengths, and the impact of these differences on the thermomechanical properties of NIPU networks was examined. The methoxy groups present in the lignin-derivable cyclic carbonates led to thermosets with significantly improved toughness (similar to 49-59 MJ m(-3)) and elongation at break (epsilon(b) similar to 195-278%) vs. the BPA/BPF-based benchmarks (toughness similar to 26-35 MJ m(-3), epsilon(b) similar to 86-166%). Furthermore, the addition of dimethyl substitution on the bridging carbon resulted in increased yield strength (sigma(y)) - from similar to 28 MPa for networks with unsubstituted bridging carbons to similar to 45 MPa for the dimethyl-substituted materials. These enhancements to mechanical properties were achieved while retaining essential thermoset properties, such as application-relevant moduli and thermal stabilities. Finally, the triamine crosslinkers provided substantial tunability of thermomechanical properties and produced NIPUs that ranged from rigid materials with a high yield strength (sigma(y) similar to 65-88 MPa) to flexible and tough networks. Overall, the structure-property relationships presented highlight a promising framework for the design of versatile, bio-derivable, NIPU thermosets.