The introduction of functional groups such as vinyls and carboxylic acids in technical lignin is particular useful for further polymer synthesis. In this study, a two-step greener procedure was used for functionalization of lignin bearing terminal vinyl compounds or terminal carboxylic acids, replacing traditional unsustainable routes; the procedures avoided toxic solvents and halogen-based reagents. Because previous research showed that the esterification reaction using organic acids and cyclic anhydride compounds could only selectively react with aliphatic OH groups, lignin was first hydroxyalkylated; ethylene carbonate was used as solvent and reagent to obtain hydroxyethyl lignin (HELignin, 90% aliphatic OH functional content). For introducing vinyl groups, the aliphatic OH groups in HELignin was successfully esterified by unsaturated organic acid at 90~160 °C. In this process, the organic acid was used as solvent and reagent without adding catalyst. Results showed that the degree of substitution of hydroxyls with the vinyl content is between 60-90%, depending upon reaction conditions based on <sup>13</sup>C nuclear magnetic resonance analysis. For introducing carboxylic acids, glutaric anhydride was used as solvent and reagent to modify HElignin, with 1-methylimidazole as a catalyst. Results showed that the esterification of aliphatic hydroxyl groups with conversion into acid functionality can reach 90% based on <sup>31</sup>P nuclear magnetic resonance analysis. Moreover, the molecular weight and thermal properties of these modified lignins were further studied suggesting limited side reactions. Overall, the HELignin is a robust platform for further greener and high-efficient functionalization of lignin, in the preparation of potentially more sustainable precursors for polymeric materials.

Hydroxyethyl lignin: a robust building block for greener modification of lignin with carboxylic acid and vinyl functionality

2019 Spring National Meeting

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