Synthesis And Characterization Of Soluble Polyimides Containing Tert-Butyls And Flexible Units

Polyimides（PIs）are a class of high performance polymer materials with excellent comprehensive properties and can be used in many high-tech fields,including motorcars,machines,spaceflights,electronics,and separation membranes etc.The rigid imide ring endows PIs with excellent thermal stability and mechanical property,but also brings about poor solubility and difficult processing,which limited their further commercial applications.In order to overcome above-mentioned problems,more attention has been focused on design and synthesis of novel PIs with good solubility and excellent processing without sacrificing outstanding inhererent properties.In this paper,we first summarized the development,synthetic methods,properties and applications of polyimides,and then mainly focused on the structural modification methods to improve the solubility of polyimides.On the base of the rule―Structure determines nature for polymers.‖,two novel aromatic diamines containing tert-butyl and flexible units were designed and synthesized.Then they were polymerized with some commercial aromatic dianhydrides via one-pot method to afford a series of polyimides with good solubility and high transparency.The chemical structure of the diamines and resutling PIs was confirmed by NMR,FTIR and EA measurements.The physical properties of the resulting PIs were also studied by UV-Vis,DSC,TGA and tensile tester etc.The detailed research contents and results were descried as follows:1.The aromatic diamine monomer,2,2-bis（3’-（tert-butyl）-4’-aniline-bisphenyl-4-ehter）propane was synthesized via four steps including iodination,acetyl protection,coupling reaction and deprotection from2-tert-butylaniline and bisphenol A.Then it was polymerized with several commercial aromatic dianhydrides via one-step polycondensation method to produce a series of PIs.The NMR,FTIR and EA results confirmed the chemical structure of the resulting PIs.The PIs containing tert-butyl and bisphenol A unit exhibited an excellent solubility at room temperature in many common organic solvents,such as NMP,DMF,DMAc,THF and CHCl₃ etc.The transparency of the corresponding membranes was equal to or higher than 90%in the visible light range from 400 nm to 760 nm.The number-averaged molecular weights（M_n）of the resulting PIs were in the range from 1.9×10⁴ to 3.9×10⁴ with PDI from 2.63 to 4.63 by GPC measurement.They also displayed outstanding thermal stability with the glass transition temperature（T_g）,the weight loss temperature of 5%（T₅）and 10%(T₁₀)in nitrogen in the range of 265℃-305℃,519℃-529℃ and 527℃-536℃.In addition,the producing PIs still retained good mechanical property and low water absorption rates of 0.23%-0.42%.2.Another novel aromatic diamine monomer,4,4’-（3-（tert-butyl）-4-anmino-phenoxy）diphenyl ether,was also synthesized via the similar method as above.Then it was polymerized with various commercial aromatic dianhydrides via one-step polycondensation to produce a series of PIs with tert-butyl and multiple ether unit.Their chemical structures were verified by NMR,FTIR and EA measurements.These PIs also showed the excellent solubility,and were soluble in many common organic solvents,including NMP,DMF,DMAc,THF and CHCl₃ etc.The thermal performance,transparency and mechanical performance etc.were tested by TGA,DSC,UV-Vis and tensile tester.Their T_gs were ranged in 264-300℃,and T₅ and T₁₀ in nitrogen were above 525℃and 533℃respectively.The light transparency of PI membranes was higher than 90%in the visible light range from 400 nm to 760 nm.The tensile strengths,elongation at breaks and Young’s modulus of PIs membranes were ranged in 52-58 MPa,6.1%-10.2%and 1.94-2.48 GPa respectively.The XRD results demonstrated that these PIs were amorphous glassy polymers with low water absorption rates of 0.45%-0.66%.