Molecular Design And Electrospinning Preparation Of High-whiteness And Thermal Resistant Polyimide Ultrafine Fibers

Polyimide?PI?ultrafine fibers represent a type of high-performance polymeric fiber materials with excellent comprehensive properties.However,due to the formation of charge transfer complexes?CTC?,conventional wholly aromatic PI fibrous membranes usually have a deep color,which greatly limit their applications in advanced optoelectronic fabrications.In the current work,in order to prepare PI ultrafine fiber membranes with both of high whiteness and good thermal stability,fluoro-containing or alicyclic units were introduced into the PI molecular chains to reduce the formation of CTC.On the other hand,electrospinning procedure was carried out to obtain the PI fibrous membranes with highly disordered physical morphography,which can effectively increase the scattering of the visible light.The preparation of PI ultrafine fibrous membranes and the relationship between chemical structures and the properties were systematically studied.?1?A series of aromatic fluorinated PI resins?6FDA-PI?were synthesized by a two-step chemical imidization reaction from 4,4'-?hexafluoroisopropylidene?-diphthalic anhydride?6FDA?and four aromatic diamines containing rigid-rod moieties,respectively.FPI ultrafine membranes were successfully prepared via electrospinning procedure with the organo-soluble 6FPI-PI resins as the starting materials.The whiteness of the FPI fibrous membranes was greatly improved and whiteness index?WI?of the membranes were higher than 78.00 and reached the highest of 88.38 for FPI-2?6FDA-APBO?.In addition,the FPI ultrafine fibrous membranes exhibited excellent thermal stability,with the 5%weight loss temperatures(T_5%)over 500?,and the glass transition temperatures?T_g?higher than 345?.?2?A series of semi-alicyclic PI resins?HTABP-PI?were synthesized by the two-step chemical imidization reaction from 4,4'-dihydroxybiphenyldicyclohexane-carboxylate-3,3',4,4'-tetracarboxylic acid dianhydride?HTA-BP?and five aromatic diamines,respectively.CPI ultrafine fibrous membranes were successfully prepared via electrospinning procedure with the organo-soluble CPI resins as the starting materials.The whiteness of the CPI ultrafine membranes was significantly improved with the WI higher than 93.00 and reached to the highest 95.06 for CPI-1?HTA-BP/6FBAB?,which was much higher than those of 6FDA-PIs.The T_5%of the obtained CPI ultrafine membranes were higher than 410?,and the T_g was between 192.9?and 241.9?.The thermal stability of the CPIs was lower than that of the 6FDA-PIs.?3?A series of semi-alicyclic CPI resins containing hydrogenated naphthalene units were synthesized by the two-step chemical imidization reaction from two alicyclic dianhydrides,1,2,3,4-tetrahydro-1-naphthalene succinic dianhydride?TDA?and 3,4-dicarboxy-1,2,3,4,5,6,7,8-decahydro-1-naphthalene succinic dianhydride?HTDA?,and two aromatic diamines,respectively.The CPI ultrafine fibrous membranes were successfully prepared via the one-step electrospinning procedure.The CPI membranes showed high whiteness with the WI values higher than 93.00.The T_5%values of the obtained CPI membranes were higher than 440?and the T_g values were in the range of 231.7³21.9?.Compared with the HTABP-PIs,the thermal stability of the TDA-or HTDA-PIs membrane was improved without decreasing the WI values.Thus,the hydrogenated naphthalene-containing CPI fibrous membranes exhibited the excellent comprehensive properties.