Synthesis of\nSemiaromatic AA/BB-Type Polyamides via\nChemoenzymatic Polycondensation

Polypeptide-based AA/BB-type polyamides containing aromatic\nmoieties\nin the main chains were synthesized via chemoenzymatic polycondensation\nof diamine and diester-type aromatic monomers through the use of papain\nin aqueous buffers. To mitigate the low substrate recognition of papain\nby aromatic units, aromatic diamines, such as 1,3-phenylenediamine\n(Pda), 2,4-diaminoanisole (Dan) and 2,4-diaminophenol (Dap), and aromatic\ndiacids, such as 5-aminoisophthalic acid (Aip), were modified with\nglycine. The diamine monomers GlyPdaGly, GlyDanGly and GlyDapGly and\ndiester monomer GlyAipGly were used for polycondensation in the presence\nof papain, resulting in the formation of the AA/BB-type polyamides\npoly(GlyPdaGly-<i>alt</i>-GlyAipGly) (AP(GG)), poly(GlyDanGly-<i>alt</i>-GlyAipGly) (AP(GG)<sup>OMe</sup>) and poly(GlyDapGly-<i>alt</i>-GlyAipGly) (AP(GG)<sup>OH</sup>). Structural analysis\nof the polyamides via Fourier transform infrared (FT-IR) spectroscopy\nand wide-angle X-ray diffraction (WAXD) revealed that the AP(GG) series\nwas largely amorphous, resulting from a reduction in the hydrogen\nbonding of PolyGly due to the inclusion of aromatic moieties in the\nmain chain. Thermal analysis of the AP(GG) series revealed high thermal\nstability and thermoplasticity, which are caused by the rigid structure\nof the benzene ring and the amorphous structure of the polyamides.\nThe postpolycondensation products of AP(GG), AP(GG)<sup>OMe</sup> and\nAP(GG)<sup>OH</sup> formed hyperbranched/networked structures via\namidation of Aip amines. Notably, chemoenzymatic polymerization followed\nby postpolycondensation provided peptide-based semiaromatic polyamides\nwith high thermal stability.