Thermoreversible Diels-Alder Cross-Linking of BHMF-Based Polyesters: Synthesis, Characterization and Rheology

2,5-Bis(hydroxymethyl)furan (BHMF)-based polyesters are an interesting new class of biobased and potentially biodegradable furanic polymers. However, their thermal properties are currently insufficient, making them unsuitable for potential applications as commodity plastics. To improve this, several polyesters were synthesized using an enzymatic bulk polymerization process with the monomers BHMF and aliphatic dimethyl esters of varying spacer lengths. The BHMF units were subsequently cross-linked with a biobased bismaleimide (BM-689) through a [4 + 2] cycloaddition reaction between the furan and maleimide groups. This approach clearly demonstrated that these furan-based polyesters can be thermoreversibly cross-linked using this bismaleimide. The use of different spacer lengths further allows the variation in relative reaction rates and affects the reversibility and reprocessability of the polymers. In situ ¹H NMR spectroscopy revealed the identification of the endo- and exostereoadducts formed by the Diels-Alder reaction. A rheological analysis demonstrated the reprocessability and the thermal properties were further characterized via thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). This study sheds light on the thermal and mechanical enhancement of biobased BHMF-based polyesters, while maintaining their recyclability, which widens the range of potential application of this promising polymer.