Chemoenzymatic Polymerization/Depolymerization of Semiaromatic Polyamides for Chemical Recycling

Chemical recycling of polymeric materials represents a promising approach for achieving sustainable material cycles, yet conventional chemical recycling based on depolymerization methods often requires harsh conditions and is limited in the narrow scope of available polymers. In this study, novel semiaromatic polyamides consisting of 4-amino-3-hydroxybenzoic acid (Ahb) and peptide moieties were enzymatically synthesized by papain-catalyzed polymerization in aqueous media. The monomer sequence significantly affected polymerizability, with GlyAhbGly, AlaAhbGly, and SerAhbGly sequences successfully yielding their corresponding polyamides under mild enzymatic conditions. Wide angle X-ray diffraction analysis revealed that the periodic sequences determined the crystalline structures of the polyamides, indicating that selecting appropriate amino acid residues can tune their physical properties. All the polyamides showed enzymatic degradation behavior in aqueous protease solutions, and particularly those with AlaAhbGly and SerAhbGly sequences underwent sequence-selective degradation into their corresponding monomer units when treated with proteinase K. The mild enzymatic polymerization and depolymerization of the semiaromatic polyamides will offer a chemical recycling approach for polyamide materials that are difficult to break down into monomers through a conventional thermal process.