High-performance polyimine vitrimers from an aromatic bio-based scaffold

Abstract

Bio-based vitrimers represent a promising class of thermosetting polymer materials, pairing the recyclability of dynamic covalent networks with the renewability of non-fossil fuel feedstocks. Vanillin, a low-cost lignin derivative, enables facile construction of polyimine networks marked by rapid exchange and sensitivity to acid-catalyzed hydrolysis. Furthermore, the aromatic structure makes it a promising candidate for the design of highly aromatic networks capable of high-performance thermal and dimensional stability. Such properties are paramount in polymeric thermal protection systems. Here, we report on the fabrication of polyimine networks with particularly high aromatic content from a novel trifunctional vanillin monomer prepared from the nucleophilic aromatic substitution of perfluoropyridine (PFP) on a multi-gram scale (>20 g) in high yield (86%). The trifunctional aromatic scaffold was then crosslinked with various diamines to demonstrate tunable viscoelastic behavior and thermal properties, with glass transition temperatures (T_g) ranging from 9 to 147 °C, degradation temperatures (5% mass loss) up to approximately 370 °C, and excellent char yields up to 68% at 650 °C under nitrogen. Moreover, the vitrimers displayed mechanical reprocessability over five destruction/healing cycles and rapid chemical recyclability following acidic hydrolysis at mild temperatures. Our findings indicate that vitrimers possessing tunable properties and high-performance thermomechanical behavior can be easily constructed from vanillin and electrophilic aromatic scaffolds for applications in heat-shielding materials and ablative coatings.

Fig. 1. Synthetic scheme and conditions with key features of tris(vanillyl)-3,5-difluoropyridine (TVnFP) monomer synthesis.

Fig. 2. Compression molding of vitrimer particles from networks of trivanillin monomer crosslinked with (A) m-xylylenediamine (TVn-X), (B) hexamethylenediamine (TVn-H), (C) diaminododecane (TVn-D), and (D) Priamine (TVn-P). Resultant disk and bar geometries indicate excellent healability with minimal defects and high transparency.

Fig. 3. (A) Stacked differential scanning calorimetry (DSC) plots with marked T_g values of networks crosslinked with m-xylylenediamine (TVn-X), hexamethylenediamine (TVn-H), diaminododecane (TVn-D), and Priamine (TVn-P) showing excellent tunability over a wide temperature range. (B) Overlayed FTIR spectra of vitrimers with trivanillin monomer (TVnFP), indicating near full disappearance of the aldehyde carbonyl stretch and clear emergence of characteristic imine stretch.

Fig. 4. Thermogravimetric analysis (TGA) plots (under N₂) of networks crosslinked with m-xylylenediamine (TVn-X), hexamethylenediamine (TVn-H), diaminododecane (TVn-D), and Priamine (TVn-P) indicating excellent stability and outstanding charring behavior.

Fig. 5. DMA thermograms of networks crosslinked with (A) m-xylylenediamine (TVn-X), (B) hexamethylenediamine (TVn-H), (C) diaminododecane (TVn-D), and (D) Priamine (TVn-P) showing tan(δ) peaks consistent with T_g values from DSC and constant rubbery plateau moduli indicating constant crosslink density. Inset images of vitrimer bar used in experiments.

Fig. 6. (A) Creep-recovery experiments for networks crosslinked with m-xylylenediamine (TVn-X), hexamethylenediamine (TVn-H), diaminododecane (TVn-D), and Priamine (TVn-P) at 150 °C at a constant force of 5000 Pa (experiments ran in duplicate). (B) Arrhenius plots of stress relaxation data for networks (τ at G/G₀ = 1/e, in 5 °C increments). Data indicates flow behavior is dependent on diamine functionality. Vitrimer samples in triplicate.