Photocatalytic Transformation of Isotactic Polypropylene Using Phthalimide N-Oxyl Radicals Under Mild Conditions

Incorporating polar functionality into C(sp3)─H bonds in isotactic polypropylene (iPP) without compromising its molecular weight during post-polymerization modification has long been a challenge due to competing chain degradation reactions. Here, a facile, radically mediated approach is presented that enables chain functionalization without chain scission. To achieve this, a photocatalytic process is designed that operates under mild conditions, maintaining iPP in a gel state. Using a reusable immobilized photocatalyst under 455 nm light and N-hydroxyphthalimide (NHPI) as a cocatalyst, the method uses active and stable phthalimide N-oxyl radicals (PINO) to activate iPP gels via a hydrogen atom transfer (HAT) at temperatures as low as 50°C, followed by chain functionalization. Based on the comprehensive synthetic, structural, rheological, surface, and mechanical studies, it is demonstrated that controlling NHPI-to-radical scavenger stoichiometry under inert conditions enables maleic anhydride functionalization of industrial iPP regioselective to tertiary carbon without any loss in molecular weight. This approach is further extended to upcycle iPP by fully deconstructing it into narrowly dispersed hydrocarbons through a cascade of chain scissions under 367 nm irradiation. Building on molecular functionalization, the interfacial activity of PINO is revealed, allowing for direct solid surface functionalization in water, hereby creating polar interfaces with exceptional stability.