Lignin-based polyurethane prepolymers, polymers, related compositions, and related methods

Abstract

The disclosure relates to a polyurethane prepolymer and corresponding crosslinked network polymer incorporating lignin as a natural polyol in the polyurethane system. The polyurethane prepolymer includes a reaction product between an isocyanate, lignin, and a cyclic alkyl carbonate. The reaction product includes (i) free isocyanate groups and/or free hydroxyl groups, (ii) urethane linking groups between residues of lignin aliphatic hydroxyl groups and the isocyanate, (iii) ester linking groups between residues of lignin aromatic hydroxyl groups and a ring-opened form of the cyclic alkyl carbonate, and (iv) optionally urethane linking groups between residues of the ring-opened cyclic alkyl carbonate and the isocyanate. The polyurethane polymer can be a networked, crosslinked polymerization product of the prepolymer reaction product, for example in combination with a lignin curing agent. The polyurethane polymer can be used as a coating on a substrate, an adhesive joining multiple substrates, etc.