Molecular Design Enhances the Insulation and Corona Resistance Properties of Polyimide/Fluorinated Boron Nitride Nanosheets Composites

New energy vehicle drive motors are developing in the direction of high specific power, high voltage, and high-frequency pulsewidth modulation, which puts forward higher requirements on the insulation and corona resistance of electromagnetic wire enamel for drive motors. At present, modified polyimides are used as the main corona resistance materials for electromagnetic wires. In this article, a highly crosslinked sulfone-containing polyimide (3ANSPI) is designed and prepared by introducing a sulfone group and a ternary amino group. The graft modification of boron nitride nanosheet (BNNS) with 4-trifluoromethyl phenylacetic acid (4-TFPA) is further utilized to investigate the effect of fluorine content on the insulation and corona resistant of highly cross- linked sulfone-containing polyimide/fluorinated BNNS composites. The results show that when the molar ratio of ODA to diaminodiphenyl sulfone (DDS) is 15:1, PMDA to DSDA is 25:1, and the total molar ratio of ODA and DDS to triaminopyrimidine (TAP) is 35:1, the mass of BNNSs is 1%, and the concentration of 4-TFPA is 3%, the performance of the highly crosslinked sulfone-containing polyimide/fluorinated BNNS composites is optimal. The breakdown field strength increases to 696.3 kV/mm at room temperature, which is 1.67 times higher than that of conventional PI. Corona-resistant lifetime is up to 25.5 min at room temperature and 20 kHz, which is 6.54 times higher than conventional PI (3.9 min). This study provides an effective solution for the preparation of polyimide electromagnetic wire enamel with high insulation and corona resistance properties, which is expected to promote the development of electromagnetic wire enamel for drive motors.