Bio-based vitrimers from divanillic acid and epoxidized soybean oil

Divanillic acid (DVA), a symmetrical dimer of vanillic acid, is a novel aromatic building block for bio-based polymers. In the present study, we prepared DVA-derived crosslinked vitrimers, which constitute a new class of thermosetting polymers formed via dynamic covalent bonds. We cured two series of bio-based vitrimers, OHESO-x and BuESO-x (x represents the COOH/epoxy ratio, x = 1.5, 1.0, 0.7) derived from DVA and butoxylated DVA, respectively, with epoxidized soybean oil (ESO) in the presence of a transesterification catalyst. Depending on the side chain structures and x values, the glass transition temperatures (Tgs) and Young's moduli of the vitrimer films varied from 20 to 62 degrees C and from 3 to 286 MPa, respectively. The OHESO-x vitrimers had higher Tgs and Young's moduli than the BuESO-x vitrimers with the same x values. This was due to the hydrogen bonds formed by the free phenolic hydroxyl groups and unreacted carboxylic acid groups. We confirmed dynamic transesterification by stress relaxation testing, and characterized the reprocessability and self-healing properties of the vitrimers. Bio-based vitrimers based on dynamic transesterification were cured from divanillic acids and epoxidized soybean oil. These materials exhibited satisfactory thermal and mechanical properties, and could be reprocessed at high temperatures.