Preparation Of Polyimide Ultrafine Fibrous Membranes Via Ultraviolet-assisted Electrospinning Procedure

Polyimide(PI)electrospun ultrafine fiber membranes(UFMs)were usually prepared by a two-step precursor method or a one-step soluble PI method.However,the former often leads to fiber morphology defects in the process of high-temperature imidization and dehydration,while the latter leads to poor solvent resistance of the fibers.In order to give PI UFMs good morphology and solvent resistance,an ultraviolet assisted electrospinning(UVAES)technology was designed.By using negative photosensitive polyimide(PSPI)or its precursor as the starting material,the in-situ photo-crosslinking reactions induced by ultraviolet radiation give PI UFMs good comprehensive performances.The relationship between the structure and properties of PI UFMs was systematically studied,and the solvent resistance was studied emphatically.Firstly,a photosensitive polyamic(acid ester)(PSPAE)was designed and synthesized,and researches on the preparation of PI UFMs by the UVAES process was carried out.PSPAE resin was prepared by 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride(ODPA),4,4'-diaminodiphenyl ether(ODA)and hydroxyethyl methacrylate(HEMA).The electrospinning solution was prepared by adding photoinitiator and crosslinking agent.Photo-crosslinked PSPAE fibrous membrane was obtained by UVAES technology,and then converted into PI UFM by thermal imidization at 350?.The diameter of the PI UFM is about 1-3?m,the glass transition temperature(T_g)is higher than 250?,and the 5%mass loss temperature(T_5%)exceeds 480?.The prepared PI UFM can maintain its fibrous morphology after immersed in N,N-dimethylformamide(DMF)for 60 s.Secondly,organic soluble intrinsically photosensitive polyimide(PSPI)resin was designed and synthesized,and researches on the preparation of PI UFMs by UVAES process was carried out.By utilizing 3,3',4,4'-benzophenonetetracarboxylic dianhydride(BTDA)and two ortho-alkyl containing aromatic diamine monomers,PSPI was prepared by one-step high-temperature solution polycondensation.The PI UFMs were directly prepared by the UVAES method.The average diameter of the prepared PI UFMs is less than 500 nm,the T_g is higher than 400?,and the T_5%is over 440?.This series of PI UFMs can maintain the original fibrous structure after soaked in DMAc for 60 s.Finally,two fluorine-containing intrinsic PSPI resins were designed and synthesized,and the researches on the preparation of PI UFMs by UVAES process was carried out.PSPI was prepared by one-step high-temperature polycondensation method by BTDA and two kinds of aromatic diamines containing methyl at the ortho position,with benzene and trifluoromethyl as side chains.PI UFMs were prepared by the UVAES method.The prepared UFMs have an average diameter of200-300 nm,T_g higher than 400?,and T_5%higher than 440?.This series of PI UFMs can maintain the original fibrous structure after immersed in DMAc for 60 s.