Efficient Synthesis of Chemically Recyclable Polyamides via Substituent Effects-Enabled Mechanistic Pathway.

Imination and amidation are two fundamental condensation reactions central to modern chemical synthesis, and devising energy-efficient ways to trigger them is highly relevant in advancing low-carbon manufacturing, with most approaches relying on the use of catalysts. Here, we revisit the dimethyl acetone-1,3-dicarboxylate (DADC) chemistry, and show that it can react with a broad range of small-molecule and macromolecular amines at moderate temperatures (80‒120 °C) in the absence of any catalysts. This represents a significant reduction in processing temperatures compared to traditional polycondensation methods for polyamide synthesis, which often require temperatures exceeding 230 °C. Mechanistic and model studies reveal that the high reactivity of DADC toward amines arises from its synergistic substituent effects; Specifically, the two ester groups in the symmetric β-position of DADC's ketone facilitate initial imination via conjugation and electron-withdrawing effects, generating a β-enamino intermediate. This β-enamine subsequently engages in intramolecular hydrogen bonding with one ester group, reducing steric hindrance on the remaining ester and thus promoting its amidation. Moreover, we demonstrate that the DADC-synthesized polyamides are thermally reprocessable, and chemically recyclable under either acidic or basic conditions at mild temperatures, and the chemical recycling is possible both for the neat polymer and its mixture with other plastics.