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Abstract We report synthesis of a radical scavenging aminated thermoplastic polymer through reactive extrusion of polyethyleneimine (PEI) with a polypropylene and polypropylene‐graft‐maleic anhydride (PP‐g‐MA) meltblend. The reaction was confirmed using acid orange 7 (AO7) amine density assay, toluidine blue O (TBO) carboxylic acid density assay, Fourier transform infrared spectroscopy (FTIR), and a migration assay. FTIR spectra revealed a reduction of the asymmetric stretching of the maleic anhydride (MA) carbonyl group at 1777 cm⁻¹and the emergence of the maleimide carbonyl peak at 1702 cm⁻¹. AO7 supported surface orientation of grafted amine groups by introduction of 7.22 nmol cm⁻²primary amines, corresponding to the reduction of surface carboxylic acids quantified by TBO from 12.46 nmol cm⁻²to 0.43 nmol cm⁻². After incubation (40°C, 10 days) in ethanol, acetic acid, and water, < 0.1 mg cm⁻²PEI migrated from the materials, supporting the covalent nature of the grafting. Antioxidant activity was demonstrated exhibiting 5.90 and 4.31 nmol Trolox_eqcm⁻²in aqueous and organic environments, respectively. Results indicate a successful condensation reaction during reactive extrusion, producing an aminated thermoplastic polymer with antioxidant activity for target applications such as food packaging, wastewater treatment, carbon capture, and others.