The Synthesis And Characterization Of Three-Dimensional Cross-Linked Wholly Aromatic Polyimide

Aromatic polyimides have been widely utilized because of their excellent comprehensive characters and easy synthesis since 1960s.Recently,in the field of microelectronics and Hstorage porous PIs are high-lighted.As a potential candidate,cross-linked PIs are drawing much attention since they process stereo regularity as well as thermal and chemical stability.A rigid tetrafunctional amine,tetrakis(4-aminophenyl)methane(TAPM),and a difunctional acid,2,5-bis(ethoxycarbonyl)terephthalic acid(ECTA),were synthesized as crosslinkers.Two precursors,s-PEA and g-PEA,were obtained in two different ways,ionic self-assembly and sol-gel method,by reacting from TAPM and ECTA.Afterwards, imidization of these two precursors were carried out to abtain crosslinked PIs.The structures of the monomers,precursors and PIs were characterized by FTIR,~1H NMR,MS and melting point test.The crystal morphology of s-PEA was viewed from Wide-angle x-ray diffraction (WXRD).The process of ironic self-assembly was tracked by FTIR.Differential scanning calorimetry(DSC),thermogravimetric analysis(TGA) and FTIR were utilized to tract the process of imidization.The FTIR track of ionic self-assembly process reveals that amido of TAPM is protonized by reacting with carboxylic acid of ECTA in polar aprotic solvent which leads to the formation of ionic bond.The molecular grow with the formation of ionic bond and become less soluble.Ultimately,the s-PEA is precipitated from the solvent.The FTIR,DSC and TGA test of imidization of s-PEA and g-PEA indicates that the imidization mechanism of the two precursors is different.The former includes transformation from ionic bond to covalent bond of amic ester,which is a stereospecific polymerization.In this case,the curing kinetics and curing procedure are inconsistent.The spacial structures of PIs synthesized by two ways were charactered by WXRD.