Vanillin-Based Degradable Polyurethane Thermosets Demonstrating High Bio-Content and Mechanical Properties

Polyurethanes are widely used polymeric materials, butthey arerarely biorenewable and degradable. Although some previously reportedbio-based polyurethanes exhibit good thermal and mechanical properties,their bio-content is usually low, resulting from the only replacementof the diol monomer instead of the whole diol/diisocyanate pairs.In addition, traditional polyurethanes are often difficult to degrade,leading to environmental issues. To address these issues, we proposea solution by sourcing both the diols and isocyanates from biorenewableresources and introducing degradability into diols via the Tishchenko reaction, which is the disproportionation of twoaldehydes to afford an ester bond with an atom economy of 100%. Commerciallyavailable bio-based vanillin was selected as the precursor for a vanillin-baseddiol (VBD) containing ester bonds. By reacting VBD with l-lysine diisocyanate (LDI) and trimethylolpropane (TMP) as a crosslinker,a series of bio-based thermosetting polyurethanes, VBD-TMP (x) , with high bio-based carbon content (>70.0%)were synthesized. The chemical structures and properties of monomersas well as polymers were characterized using nuclear magnetic resonance(NMR), Fourier transform infrared (FTIR) spectroscopy, thermogravimetricanalysis (TGA), differential scanning calorimetry (DSC), dynamic mechanicalanalysis (DMA), and tensile tests. The obtained VBD-TMP (x) polyurethanes exhibit comparable mechanical properties(sigma = 32.0 MPa; E ' = 2.7 GPa) to commercialthermosetting polyurethanes and demonstrate higher toughness (34 MJ/m(3)) than previously reported bio-based analogues. Additionally,the inherent ester bond in the VBD monomer enables the complete degradationof VBD-TMP (x) in a 0.1 M NaOH solution (THF/H2O = 1:1, v/v) within 3.5 h. This greatly broadens the availableend-of-life choices, including the recovery of the monomers. Thisstudy presents a facile approach for creating degradable polyurethanematerials with high bio-content and mechanical properties.

Automated summary

This study presents a simple and effective approach to synthesize degradable polyurethanes with high bio-based carbon content and desirable mechanical properties by sourcing diols and isocyanates from biorenewable resources and introducing degradability via the Tishchenko reaction. The obtained polyurethanes can be completely degraded in a NaOH solution, expanding the end-of-life options.