Tailoring Crystalline Morphology in Polypropylene via Ethylene Sequence Engineering for Enhanced DC Breakdown Strength

Polypropylene (PP) has emerged as a promising candidate for cable insulation in high-voltage direct-current (HVDC) transmission systems due to its high working temperature and exceptional electrical properties. Through ethylene sequence engineering, the crystallization behavior of PP is modulated by strategically incorporating ethylene comonomer units into the polymer backbone, thereby tailoring the crystalline morphology and reducing spherulite dimensions to optimize dielectric performance. The controlled distribution of ethylene segments disrupts long-range chain ordering, refining the crystalline–amorphous interface and suppressing space charge accumulation. At 90 °C, the average DC breakdown strength of PPR was enhanced by 25 and 28% compared to PPH and PPB, respectively. This significant improvement is attributed to the semicrystalline microstructure resulting from ethylene sequence engineering. These findings provide a molecular-level design strategy for high-voltage insulating materials, balancing crystalline morphology control and dielectric properties.