Melt Grafting of Geometry-Tailored Voltage Stabilizers for High-Performance Polypropylene Insulation

High-performance polypropylene (PP) insulation is essential for next-generation high-voltage direct current (HVDC) systems. This study presents a scalable, solvent-free melt grafting strategy to covalently incorporate thermally stable aromatic voltage stabilizers (VSs)—2-vinylnaphthalene (VN), 1,1-diphenylethylene (DPE), and 4-vinylbiphenyl—into isotactic PP. VSs are rationally selected based on their high boiling points, π-conjugated aromatic structures, and vinyl functionality, enabling compatibility with melt processing and uniform bulk functionalization of PP. Electrical tests showed that VN and DPE markedly improved volume resistivity, suppressed leakage current, and enhanced DC breakdown strength, while their effects diminished at loadings above 1.0 wt.%, respectively. Thermally stimulated depolarization current confirmed that these gains originated from deeper and well-distributed trap formation. Quantum chemical and finite element simulations further revealed how geometry-tailored VSs modulate trap formation and suppress space charge accumulation, linking molecular-scale trapping to macroscopic charge dynamics. This work highlights a practical and recyclable route to engineer PP insulation with superior insulation reliability, offering new insights into stabilizer structure-property relationships for HVDC applications.