Enhanced Polyacrylamide Degradation via OH Radical-Initiated Single-Electron Transfer

Hydroxyl (OH) radicals, as common radicals in aqueous environments, play an important role in inducing the degradation reactions of polymers. However, understanding the fundamental mechanisms of radical-induced degradation of polymers at the atomic level remains a formidable challenge. In this study, we employ density functional theory to investigate the geometric and electronic structural properties of polyacrylamide (PAM) in (-CH2CHCONH2-)(n) (n = 2-6) complexes. Additionally, we explore the degradation mechanism of the n = 4 complex induced by the OH radical. The results indicate that there are three sites for the initial reaction (R1 and R2 are at the ends and R3 is in the middle). The OH radical removes a H atom from the PAM main chain and simultaneously triggers a single-electron-transfer process on the same chain. This process significantly reduces the dissociation energy barrier of the C-C bond in the PAM chain, from similar to 90 to similar to 20 kcal/mol. Specifically, when the induced reaction occurs at the end of the chain, a series of broken bonds will appear only along the main chain. While it happens in the middle, the broken bonds will exist simultaneously along both the main and side chains. Our results reveal the importance of OH radicals in polymer dissociation, particularly in PAM, and emphasize the degradation mechanism of SET.