Bio-based vitrimers from divanillic acid and epoxidized soybean oil

Abstract

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 (T_gs) and Young's moduli of the vitrimer films varied from 20 to 62 °C and from 3 to 286 MPa, respectively. The OHESO-x vitrimers had higher T_gs 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.