(43a) Lignin Resources As a Platform for Developing High Performance Polymers

Lignin is a widely available bioresource, yet is underutilized for production of chemicals and polymers. Model compounds derived from lignin depolymerization were investigated as sustainable sources to produce two classes of degradable polymers with high performance properties: epoxy resins and super engineering plastics. Epoxy resins are thermoset polymers widely used in composites, coatings and adhesives, with applications spanning automotive and aerospace industries, structural components, and wind turbine blades, among others. Vanillic acid, syringic acid, and 4-hydroxybenzoic acid, products of lignin depolymerization, were investigated as replacements for conventional diglycidyl ether of bisphenol A (DGEBA) in anhydride-cured epoxy resins. The resulting lignin-based epoxy resins exhibited high glass transition temperatures and similar elongation at tensile behavior as compared to DGEBA-based epoxy resins. The lignin-based epoxy resins exhibited rapid degradation, in contrast to the slow degradation rate of the DGEBA-based epoxy resin. Additionally, a series of partially bio-based spiro polycycloacetals were synthesized using lignin-derived feedstocks, such as vanillin and its derivative syringaldehyde, along with pentaerythritol and commercially available co-monomers including 4,4′-difluorobenzophenone and bis(4-fluorophenyl) sulfone. These spiro polycycloacetals displayed extremely high thermal stabilities and glass transition temperatures. Importantly, these polymers were effectively degraded to small molecules under acid-catalyzed hydrolytic conditions.