Mechanism of NH₃ and CO₂ Gas Release during Polyacrylamide Degradation

The growing severity of environmental pollution has raised broad concerns over plastic degradation mechanisms. However, a lack of atomic-level understanding has hindered progress in controlling such processes. This study investigates the radical-induced degradation mechanism of polyacrylamide (PAM) by •H and •OH radicals, focusing on the formation of NH₃, H₂O, and CO₂, and subsequent cascade degradation pathways through density functional theory. Key findings include the following. Small molecule formation has a positional preference during PAM degradation. NH₃ formation and H₂O formation preferentially occur at the acylamino in the middle of the PAM chain, while CO₂ release favors the end site of the chain. All systems follow the general energy trend "NH₃/H₂O formation is easier → CO₂ release is more difficult", with a noticeable energy barrier jump during CO₂ elimination. After the release of CO₂, the unsaturated carbon undergoes single-electron transfer (SET), leading to C-C bond cleavage and structural rearrangement. Notably, the SET process shows a minimal dependence on the molecular structure or radical attack position and is primarily governed by local electronic configuration. These insights reveal the fundamental role of SET in PAM degradation and offer theoretical guidance for designing controllable degradation strategies in complex environments.