The electrical properties of polypropylene (PP) insulation material decrease dramatically at high temperature

which limits its application in harsh environments. This study investigates how grafting styrene (St) improves the high-temperature electrical properties of PP. Compared with pure PP

the space charge of the St-grafted PP (PP-g-St) samples is suppressed

the volume resistivity is significantly improved

and the breakdown strength at room temperature (30°C) and high temperature (90 and 110°C) is increased by 35.04%

36.98% and 34.86%

respectively. The results show that the side chains generated by grafted St can increase the number of spherulites and improve the crystallinity

making the boundaries of the spherulites tortuous and narrow

which is not conducive to the formation of low-density regions. At the same time

because of the entanglement of grafted side chains and the presence of deep traps inside the PP-g-St samples

which inhibit the injection and migration of carriers

the effect of high temperature on the free volume is weakened. Consequently

the ability to capture charges at high temperature is enhanced

leading to an improvement in the high-temperature electrical properties of PP. This research can provide a reference for the development of high-performance grafted PP insulation materials.