Regioselective synthesis of lignin-derived dianilines for high-performance polyurethane-urea elastomers

Abstract

Primary anilines, especially dianilines, are the fundamental building blocks in the field of fine chemicals and materials. Lignin is an abundant renewable aromatic compound resource in nature; its high-value utilization plays a crucial role in enhancing the economic feasibility of biorefinery. Efficient production of dianilines from lignin is highly desired, but extremely challenging. In this study, an innovative strategy for the sustainable production of dianilines from lignin-derived phenolic monomers was reported. Regioselective synthesis of m,m′-, o,m′- and o,o′-dianilines via a Smiles rearrangement–condensation sequence or a condensation–Smiles rearrangement sequence was systematically compared. The hitherto unconsidered isomerization and acid-catalyzed cleavage mechanism among m,m′-, o,m′- and o,o′-bisphenols was reported. The “stepwise amination” process was proposed for the Smiles rearrangement of bisphenols according to density functional theory (DFT) calculations. Furthermore, the lignin-derived m,m′-, o,m′- and o,o′-dianilines were applied as sustainable chain extenders in the manufacture of polyurethane-urea elastomers and their effects on the properties of the polymers were investigated. Lignin-derived o,m′-dianiline exhibited superior mechanical properties compared to the traditional petroleum-based dianiline chain extenders methylene diphenylamine (MDA) and 4,4′-methylene-bis-(2-chloroaniline) (MOCA), suggesting the application potential of lignin-derived dianilines in the field of materials.