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An ultraviolet‐assisted electrospinning (UVAES) method was investigated to improve the solvent stability of soluble polyimide (PI) electrospun ultrafine fibrous membranes (UFMs) to assist in the development of fibrous polymeric materials with improved resistance to harsh environmental conditions and to expand the potential applications for such soft filaments. A preimidized soluble negative photosensitive polyimide (PSPI) was synthesized via an one‐step thermal polycondensation from 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride (BTDA) and 1,1′‐bis(4‐amino‐3,5‐dimethylphenyl)‐1‐(3′‐trifluoromethylphenyl)methane (TFMDA). The PI resin was then fabricated into UFMs by both conventional electrospinning (ES) and UVAES with N,N‐dimethylacetamide (DMAc) as the solvent. During spinning, photo crosslinking reaction occurred, accompanied by simultaneous micro‐jets of PI‐UV ultrafine fibers in the UVAES procedure. This created fibers that were thermally stable at higher than 500°C, reflection over 77% of the 457‐nm‐ wavelength light, whiteness index (WI) higher than 83, and enhanced solvent resistance in DMAc. Generally speaking, compared with the PI UFMs fabricated by conventional ES procedure, the PI‐UV UFMs obtained by the newly‐developed UVAES procedure showed much superior solvent resistance, comparable thermal stability, slightly decreased optical reflectance and WI values, and reduced fiber diameters. These properties are of great value to future applications in microelectronics and wearable technology.

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