A Molecular Modeling Study on the Propagation in Free Radical Chain Oxidation of (B)PEI

Air oxidation of PEI is a Free Radical Chain Autoxidation process, described as a process following the Basic Autoxidation Scheme with Initiation, Propagation and Termination as discriminating steps. Molecular Modeling was able to identify the most important propagation reactions. HO₂(d) is the most likely candidate as the main oxidation chain carrying radical. α-H-abstraction from PEI α-amino hydroperoxides by HO₂(d), leading to amide PEI repeat units and eventually to HO₂(d) again, is the first step in Propagation. Apart from well-know propagation reactions, the reaction of PEI α-amino CH(d) radicals with H₂O₂ is of major importance, too, with an estimated contribution of ~50% to Propagation. Furthermore, it provides an explanation for the formation of NH₃ and various imine PEI repeat units. PEI α-amino alkoxy radicals might contribute to some extent to Propagation and can lead to chain breaks in PEI and the formation of CO₂. Amide and imine PEI repeat units contribute to ~90% of the fully oxidized PEI.