Abstract
BackgroundLignin dehydrogenation polymers (DHPs) are polymers generated from phenolic precursors for the purpose of studying lignin structure and polymerization processesMethodsHere, DHPs were synthesized using a Zutropfverfahren method with horseradish peroxidase and three lignin monomers, sinapyl (S), coumaryl (H), and coniferyl (G) alcohols, in the presence of hydrogen peroxide. The H monomer was reacted with G and a 1:1 molar mixture of S:G monomers at H molar compositions of 0, 5, 10, and 20 mol% to study how the presence of the H monomer affected the structure and composition of the recovered polymers.ResultsAt low H concentrations, solid-state NMR spectra suggest that the H and G monomers interact to form G:H polymers that have a lower average molecular weight than the solely G-based polymer or the G:H polymer produced at higher H concentrations. Solid-state NMR and pyrolysis–MBMS analyses suggest that at higher H concentrations, the H monomer primarily self-polymerizes to produce clusters of H-based polymer that are segregated from clusters of G- or S:G-based polymers. Thioacidolysis generally showed higher recoveries of thioethylated products from S:G or S:G:H polymers made with higher H content, indicating an increase in the linear ether linkages.ConclusionsOverall, the experimental results support theoretical predictions for the reactivity and structural influences of the H monomer on the formation of lignin-like polymers.
Highlights
Lignin dehydrogenation polymers (DHPs) are polymers generated from phenolic precursors for the purpose of studying lignin structure and polymerization processes
Lignin dehydrogenation polymer synthesis yields and thioacidolysis Polymers synthesized readily from H and G monomers and solids were collected with yields around 70 wt%
The amount of H-thioethylated products yielded from the H polymer, reported in Table 1, represented a small fraction of the polymer, indicating the H monomer did not form an abundance of linear, unbranched β-O-4 linkages
Summary
Lignin dehydrogenation polymers (DHPs) are polymers generated from phenolic precursors for the purpose of studying lignin structure and polymerization processes. Efforts have been made to reduce biomass recalcitrance by decreasing the total amount of lignin present, by changing the ratio of monomers and by modifying the types of linkages that occur in the lignin polymers [6, 7]. The incorporation of the coumaryl (H) monomer in lignin in biomass could result in a decrease in the molecular weight of lignin and subsequently lead to reduced biomass recalcitrance [4]. Computational studies have indicated that the incorporation of the H monomer into lignin polymers results in the formation of dilignol compounds that do not support chain elongation [8]. The H monomer has been implicated to act as a “capping” agent that stops the polymerization of lignin and results in lower molecular weight polymers. Observations have shown that biomass containing highH monomer content in the lignin may contain mostly H lignin-like polymers that separate from the rest of the lignin S:G framework [4]
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