Biobased, Nonisocyanate, 2K Polyurethane Coatings Produced from Polycarbamate and Dialdehyde Cross-linking

Bioderived polycarbamates were cross-linked with petrochemically derived and biomass-derived dialdehydes to form nonisocyanate polyurethanes (NIPUs). The bioderived polycarbamates were synthesized from a soybean oil-derived alkyd polyol and epoxidized sucrose soyate polyol via transcarbamoylation. The polycarbamates were cross-linked with 1,4-cyclohexanedicarboxaldehyde and 2,5-diformylfuran (DFF) to form coatings under either laboratory ambient conditions or through an elevated temperature cure. The coatings were characterized spectroscopically, thermally, and via standard ASTM-coating characterizations. The coatings cured under ambient conditions had similar properties to those subjected to the elevated temperature cure. Ambient-cured coatings exhibited fast tack-free times, T g values from 67 to 96 °C, high hardness, and good solvent resistance; however, they were brittle and had poor adhesion on aluminum substrates. Coatings cured at elevated temperatures showed increases in T g values to 75–150 °C. Coatings on pretreated steel substrates had good adhesion. This study demonstrates the potential for bioderived DFF to function as a dialdehyde cross-linker to form NIPUs with bioderived carbamate functional resins resulting in a bioderived NIPU capable of ambient curing. Given the potential to form a multitude of aldehyde-functionalized furanic structures from 5-(hydroxymethyl)­furfural, this increases the dialdehyde cross-linker options under consideration for formulation in bioderived NIPUs utilizing aldehyde-carbamate cross-linking.