Probing the Kinetic Origin of Varying Oxidative Stability of Ethyl- vs. Propyl-spaced Amines for Direct Air Capture

Amine-based adsorbents are promising for direct air capture of CO2, yet oxidative degradation remains a key unmitigated risk hindering wide-scale deployment. Borrowing wisdom from the basic auto-oxidation scheme, insights are gained into the underlying degradation mechanisms of polyamines by quantum chemical, advanced sampling simulations, adsorbent synthesis, and accelerated degradation experiments. The reaction kinetics of polyamines are contrasted with that of typical aliphatic polymers and they elucidate for the first time the critical role of aminoalkyl hydroperoxide decomposition in the oxidative degradation of amino-oligomers. The experimentally observed variation in oxidative stability of polyamines with different backbone structures is explained by the relationship between the local chemical structure and the free energy barrier of aminoalkyl hydroperoxide decomposition, suggesting that its energetics can be used as a descriptor to screen and design new polyamines with improved stability. The developed computational capability sheds light on radical-induced degradation chemistry of other organic functional materials.

Automated summary

We investigated the oxidative degradation mechanism of polyamines through quantum chemistry, simulations, adsorbent synthesis, and degradation experiments, highlighting the critical role of aminoalkyl hydroperoxide decomposition in the process. We explained the observed variation in oxidative stability of polyamines with different backbone structures by the relationship between local chemical structure and the free energy barrier of aminoalkyl hydroperoxide decomposition, providing a theoretical basis for screening and designing more stable polyamines.