Bio-Based Aromatic Polyesters Reversibly Crosslinked via the Diels-Alder Reaction

Diphenolic acid is functionalized with furfuryl amine and subsequently incorporated in a (partly) bio-based polyester through interfacial polycondensation with terepthalic chloride. The furan groups present in the resulting polyester are able to form a thermoreversible covalent network with different bismaleimide moieties via the Diels-Alder (DA) reaction. Our analysis of the polymer network by H-1-NMR clearly shows the formation of both possible stereoisomers (endo and exo) from the Diels-Alder coordination of furan and maleimide. Furthermore, it was found that these isomers can be reversibly interchanged at temperatures below the reported retro Diels-Alder reaction temperature, a phenomenon often claimed but, until present, never directly observed, for thermally reversible polymeric systems. Finally, a proof of principle for reversibility and recyclability is shown.