posted on 2023-11-30, 03:40authored byJun Zhang, Ming Hao, Depeng Zhang, Xuesong Zhang, Shijun Guo, Bo Wang, Junping Xiao, Yang Gao, Xiaoan Li
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 ∼90 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.