NMR used to study the side-reactions between peroxides and antioxidants during the reactive extrusion process of the impact polypropylene

Abstract

Side reaction pathways are observed to occur between antioxidants and peroxide during the processing of multiple resin grades mediated by controlled peroxide-induced degradation of impact polypropylene. In the present work, the reaction mechanism and main by-products between antioxidants and peroxides were investigated. The results demonstrate that peroxides greatly accelerate the decomposition reactions, and the free radicals formed from peroxide decomposition react with, for example, the antioxidant AO1010 to produce dehydrogenation of phenyl propionic unit(s) at the α position (cinnamic acid ester moiety), which generates a conjugated system leading to the increased color of the product. It is the first time to confirm the cinnamic acid moiety's existence and report its NMR data. Further, this work confirms the dehydrogenation mechanism by comparison with different sterically hindered phenolic antioxidants. It also systematically summarizes the oxidation and degradation mechanism of AO168 and AO1010 under air and peroxide environments, respectively. Based on present study, clear guidelines are obtained to improve the quality of polymeric products, especially the appearance and stability, during product development.