Varying the Oxidative Functionalization of Polypropylene Films under Quiescent Conditions

The partial thermal oxidation of isotactic polypropylene (PP, mass-average molar mass, Mw ≈ 369 kDa, dispersity, Đ ≈ 5.9) was explored over a range of temperatures (150 °C ≤ T ≤ 240 °C) with the dual goal of tailoring molar mass distributions and incorporating oxidative functionality into the chains while simultaneously reducing loss to volatile products. Autoxidation under these conditions resulted in progressively increased chain scission across two oxidative regimes, termed Regimes I and II, respectively, separated by a crossover at end-functionalization per chain, fend/chain ≈ 1. In Regime I, chain scission caused a sharp 60% reduction in Mw with negligible volatile formation, whereas in Regime II, there was significant volatile release, and slower Mw reduction. With increasing oxidation, there was an increase in the concentration of unsaturated alkene chain functionality in Regime I followed by a decline in Regime II. In contrast, the number of ketones increased monotonically with oxidation across both regimes, whereas the aldehyde content remained constant. These results are consistent with our previous work on PP oxidation in an extruder with/without the flow of N2/air, which also showed the existence of two regimes─a low/no oxygen regime where chain scission dominates, and a second oxidative regime where both chain functionalization and scission are important. This work suggests a facile pathway for the addition of functional groups to PP, which can potentially enable its reuse and further conversion to new materials.