Synthesis Of Novel Diamine Monomers And Preparation Of Organosoluble Polyimides

Aromatic polyimides(PIs)are a class of high-performance polymers with excellent thermal stabilities,chemical resistance,superior mechanical and electrical properties,and they have been extensively applied in the aviation,automotive,and microelectronic industries.However,some applications of polyimides are limited by their poor solubility and high processing temperature,because of their inherent macromolecular rigidity and strong inter-chain forces.In addition,some aromatic polyimides,such as Kapton film,show strong absorption in the visible region,which might hinder their application in the liquid-crystal display and optical waveguide.The paper mainly covered the synthesis of two aromatic diamine monomers and their corresponding soluble co-polyimides via one-step solution polycondensation.From the perspective of diamines' molecular design,pendent groups,benzimidazole rings,molecular asymmetry and the non-coplanarity have been sucessfully incorporated in the polyimide backbones to afford three series of novel polyimides with improved solubiliy,relatively good optical and mechanical properties,excellent thermal stability.The main content is as follows.1.Two aromatic diamine monomers,?,?-Bis(4-amino-3,5-dimethylphenyl)phenylmethane(BADP)and 3,3',5,5'-tetramethyl-4,4'-diaminodiphenylmethane(BADM),were synthesized sucessfully via straightforward one-step procedure with high yield.The two diamines both contain 3,3',5,5'-tetramethyl group,and only BADP diamine has phenyl pendant group.Their chemical structure of the two diamine monomers were all confirmed by FT-IR,1HNMR,elemental Analysis and MS.2.Polymerization were carried out under nitrogen flow,and equimolor amounts of diamines and dianhydride monomers were used in all cases.The series of soluble polyimides PI 3a-d were prepared from equimolar ratio of diamine monomers(BIA/BADP=1:1)with four commercial aromatic dianhydride monomers via one-step high-temperature solution polycondensation procedure.The chemical struture of the synthesized PI 3a-d were confirmed by FT-IR and 1HNMR.Due to the phenyl pendant group and noncoplanar molecular structure,the organosolubility of PI 3a-d mainly depends on the kind of aromatic trtracaroxylic acid dianhydride used,especially,PI-3c and PI-3d were well soluble in strong polar solvents;such as NMP,DMAc,DMF and have improved solubilities in common polar solvents,such as CHCl3 and THF.The UV cutoff wavelength and tensile strength of PI 3a-d were in the range of 360-380 nm and in the range of 61-100MPa,respectively.They show excellent thermal stability with glass transition temperature(Tg)in the range of 411-467?,and 10%weight loss temperature in the range of 535-560? in nitrogen,and 56-70wt%residue at 900? in nitrogen.3.In order to study the effect of diamine molar ratio on the properties of polyimides,various diamine molar ratio(BIA/BADP= 3:1,1:1,and 1:3)with equimolar amount of an appropriate aromatic dianhydride,BTDA,were used to synthesize PI 4a-c via one-step high-temperature solution polycondensation.The chemical struture of the synthesized PI 4a-c were confirmed by FT-IR and 1HNMR.PI 4a-c were well soluble in in strong polar solvents,such as NMP,DMAc,DMF.Their solubilities were improved as the content of BADP was increased.The UV cutoff wavelength of PI 4a-c films were in the range of 365-37 5nm,and their transmittances after 450 nm wavelength were enhanced as the content of BADP was increased.The tensile strength and initial modulus ranged from 100-153 MPa and 1.17-3.74GPa,respectively.PI 4a-c films have excellent thermal stabilities with glass transition temperature(Tg)in the range of 381-430?,and 10%weight loss temperature in the range of 527-537? in nitrogen.Tg values increased and the thermal stabilities were decreased as the the content of BADP increased.4.In order to study the effect of the different chemical structure of the synthesized diamines on the properties of polyimides,PI 5a-c were prepared from three sorts of diamine molar ratio(BIA/BADM= 3:1,1:1,and 1:3)with equimolar amount of an appropriate aromatic dianhydride,BTDA,via one-step high-temperature solution polycondensation.The chemical struture of the synthesized PI 5a-c were confirmed by FT-IR and 1HNMR.PI 5a-c were well soluble in in strong polar solvents,such as NMP,DMAc or DMF.The UV cutoff wavelength of PI 5a-c films were in the range of 365-375nm.And their solubilities and their transmittances after 450nm wavelength were improved as the content of BADP was increased.The tensile strength and initial modulus ranged from 102.6-149.5 MPa and 1.45-5.10 GPa,respectively.PI 5a-c films have excellent thermal stabilities with glass transition temperature(Tg)in the range of 396-431?,and 10%weight loss temperature in the range of 535-545 ? in nitrogen.Compared with BADP,the diamine BADM's molar ratio have a similar effect on the properties of the two series of polyimides.Furthermore,the organosolubilities and thermal stability of PI-4 were better than that of PI-5 due to the phenyl pendant group of BADP.