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

Abstract

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 1H-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.

The Effect of Molecular Weight on the (Re)-Processability and Material Properties of Bio-Based, Thermoreversibly Cross-Linked Polyesters

“…This phenomenon has previously been reported for a furan/maleimide polyketone network [26] and a thermoreversible epoxy resin [23,43]. The shift of the endothermic peak to higher temperatures could be explained by the transition of DA adducts from the endo to the exo conformation [1,44] (the chemical structures of these adducts are provided in the Supplementary Materials). The step-in heat capacity observed for this transition instead of a proper melting/cooling peak is merely an artifact as the broad transition is cut in the DSC thermogram.…”

“…There is, however, a small negative im the total yield: the precipitation step does not yield all the polymer as the mo weight of the shortest fractions is limited and as such, they are still soluble in me Furthermore, there is a very clear effect on the chain length as shown in the GPC elu of five different batches prepared under the same experimental conditions. A signi shorter polymer is obtained when comparing the obtained PE-fur with the long-ch fur described before [1] (Figure 2). First, the presence of multiple peaks instead of a single smooth curve indica the sample consists of relatively small polymers containing relatively large mon repeating units.…”

“…Furthermore, there is a very clear effect on the chain length as shown in the GPC elugraphs of five different batches prepared under the same experimental conditions. A significantly shorter polymer is obtained when comparing the obtained PE-fur with the long-chain PE-fur described before [1] (Figure 2).…”

“…Phenol (≥99%, Sigma-Aldrich, St. Louis, MA, USA), tetra-n-butylammonium bromide (≥98%, TBAB, Fluka), terephthaloyl chloride (99+%, Acros, New Jersey, NJ, USA), NaOH (97%, Sigma-Aldrich), methanol (practical grade, Interchema, Vollenhove, The Netherlands), chloroform (anhydrous, ≥99% Lab-Scan), and 1,1 -(Methylenedi-4,1-phenylene) bismaleimide (95%, Bismaleimide, Sigma-Aldrich) were used as received. DPA-fur was prepared following a reported procedure [1].…”

“…In the past 20 years, the focus in the field of research on polymeric products has shifted toward the synthesis and application of polymers that are both bio-based and recyclable [1]. In the near future, this will become even more important due to the growing scarcity of petroleum as a feedstock for current conventional polymeric products.…”