Antioxidant and dissociation behavior of polypropylene‐graft‐maleic anhydride

Abstract Understanding the dissociation behavior of functional polymers can help tailor materials for performance in target applications. Polypropylene‐ graft ‐maleic anhydride (PP‐ g ‐MA) undergoes partial hydrolysis to form polypropylene‐ graft ‐succinic acid (PP‐ g ‐SA) due to trace atmospheric moisture during extrusion. While there have been reports on the relationship between interfacial and antioxidant properties for functional polymers, PP‐ g ‐SA's behavior has yet to be explored despite its widespread occurrence. Here, PP‐ g ‐MA was compounded with isotactic polypropylene (PP) in a twin‐screw extruder and the influence of maleic anhydride (MA) content on interfacial behavior (dissociation constant and pH dependence of radical scavenging) was determined. Precise pK a bulk values of the PP‐ g ‐SA carboxylic acids were calculated using attenuated total reflection‐Fourier‐transform infrared spectroscopy (ATR‐FTIR) titration and found to be ~7.00–7.50 depending on MA content. The extinction coefficient ratio between the anhydride and carboxylic acids was reported for the first time, which was used to determine the increasing degree of hydrolysis with increasing alkalinity. pH‐dependent radical scavenging capacity followed closely with dissociation results, with activity reaching up to 4.02 ± 0.23 Trolox Eq (nmol/cm 2 ), supporting the proposed radical scavenging mechanisms dependent on deprotonation of the carboxylic acids. This study demonstrates how dissociative properties of functional polymers can predict radical scavenging behavior in different environments.