Functional Lignin Building Blocks: Reactive Vinyl Esters with Acrylic Acid.

Introducing vinyl groups onto the backbone of technical lignin provides an opportunity to create highly reactive renewable polymers suitable for radical polymerization. In this work, the chemical modification of softwood kraft lignin was pursued with etherification, followed by direct esterification with acrylic acid (AA). In the first step, phenolic hydroxyl and carboxylic acid groups were derivatized into aliphatic hydroxyl groups using ethylene carbonate and an alkaline catalyst. The lignin was subsequently fractionated using a downward precipitation method to recover lignin of defined molar mass and solubility. After recovery, the resulting material was then esterified with AA, resulting in lignin with vinyl functional groups. The first step resulted in approximately 90% of phenolic hydroxyl groups being converted into aliphatic hydroxyls, while the downward fractionation resulted in three samples of lignin with defined molar masses. For the esterification reaction, the weight ratio of reagents, reaction temperature, and reaction time were evaluated as factors that would influence the modification efficacy.