Dynamic polymer networks designed from biobased aldehydes and amines to circularity

Starting from bio-based aldehyde-containing aromatic monomers, diamine and a series of diols, linear polyesters with pendant aldehyde groups (PEa-PEe) and crosslinked polyimine-amides (PIA) were synthesized. Compared with previously reported PIA, high biobased content is achieved by utilizing a biobased diamine, Priamine™ 1071 (PA). In addition, the linear polyesters were blended by compression molding with PIA in different proportions to initiate imine exchange between the free aldehyde-groups in the polyesters and imine-groups in PIA. The structures and thermal properties of the obtained linear polyesters and crosslinked polymers were confirmed by NMR, FTIR, SEC, TGA, DSC, DMA and rheological analyses. Compared to most previous polyimine polymers, PIA exhibited higher thermal stability, higher elongation at break (280%) and moderate tensile stress at break of 4.7 MPa. Subsequent blending with linear polyesters provided tunable properties depending on the length of the diol used for polyester synthesis. In brief, somewhat decreased elongation at break between 129 and 189% was observed, while tensile strength at break varied from 3.2 MPa to 12.1 MPa. All the crosslinked materials demonstrated good solvent resistance in common organic solvents with 94-99% gel content. The crosslinked materials showed promising mechanical recyclability with good retention of mechanical properties after repeated compression molding. Furthermore, chemical recycling of PIA was demonstrated under acidic conditions at room temperature leading to repolymerizable aldehydes and amine hydrochlorides. This promising molecular design can be further tuned by the choice of aldehydes, amines and diols to achieve required performance in combination with closed-loop recyclability.