The Synthesis And Characterization Of Polyimide Nanofibre With High Strength And High Modulus

The excellent comprehensive performance and the recent development of thepolyimide are briefly described in this paper. Strong interest attracts us to study thehigh strength and high modulus of polyimide single nanofiber, and explore the trendof mechanical properties with the change of the fiber diameter. In recent years, thepolyimide with nitrogen heterocyclic and its performance have been reported, itshows that these excellent performance relative to heterocyclic symmetry, directionand the polarity of heteroatoms. The aromatic diamine containing pyrimidine issuccessfully synthesized, and the chemical structures of the amines are confirmed byFT-IR and NMR. A series of high molecular polyamic acids (PAAs) are synthesizedwith the diamine containing pyrimidine and different dianhydrides, then electrospuninto PAA nanofibers. The PAA nanofibers are imidized in a high-temperature to forma high performance polyimide nanofiber with uniform diameter. The morphology anddegree of imidization are respectively characterized by SEM、IR. The mechanicalproperties of the single nanofiber and the stability of the polymer are respectivelycharacterized by nanofibers tension meter and thermal gravimetric analysis (TGA).1、The pyrimidine-containning diamine is synthesized via four-step reaction of4-nitrobenzonitrile and p-nitrophenylacetic acid. In order to obtain high yield, thereaction temperature, reaction time and solvent system are investigated and optimized.The results show that the target monomer has a high purity and high yield throughbeing recrystallized. The structures and purity of intermediates and final product wereconfirmed by1HNMR, FT-IR, etc.2、A series of high molecular pyrimidine-containning copolyimide precursors areprepared from rigid pyrimidine-containning diamines(PRM) and flexible4,4’-oxydianiline(ODA) with3,3’,4,4’-biphenyltetracarboxylic dianhydride(BPDA)with different ratio in low temperature. When PRM/ODA is5:5, tensile strength,tensile modulus and elongation at break of the PAA single fiber are567.77MPa,23.23GPa and20.16%, respectivily. However, the tensile strength, tensile modulusand elongation at break of the PI single nanofiber after imidization of330℃are1770.36MPa,43.22GPa and4.52%. The polyimide also has good heat resistance, theglass transition temperature of277.4℃,5%thermal weight loss of555.96℃. 3、 The polyamide acid solution are prepared from3,3’,4,4’-biphenyltetracarboxylic dianhydride(BPDA) with2,5-dimethyl-4,4’-diamino benzidine (DMB) and polyamide acid solution,4,4’-diamino diphenyl etherdiamine (ODA). The result shows that the addition of benzoyl peroxide (BPO) cangreatly improve the mechanical properties of the polyimide. When the single fiberdiameters are fluctuate form500nm to600nm, tensile strength, tensile modulus andelongation at break of the polyamic acid single nanofiber are596.80MPa,13.40GPaand22.77%. The the tensile strength of PAA single nanofiber is increased by1.5-2times with adding10%BPO, elastic modulus is2times and elongation at breaking isnearly by2times. The imidization tempertature (250℃,300℃,350℃) wasdiscussed to effect on the mechanical properties of PI single naofiber. At the sametemperature, the mechanical properties of10%-PI is higher than that of pure-PI.4、A series of high molecular pyrimidine-containning copolyimide precursors areprepared from rigid pyrimidine-containning diamines(PRM), p-phenylenediamine(PDA) and sem-flexible m-phenylenediamine (MPD) with3,3’,4,4’-biphenyltetracarboxylic dianhydride(BPDA) with different ratio in low temperature, while the PRM isfixed on50%. When PDA/MPD is4:6, the tensile strength of copolymerizedpolyimide fiber membrane reaches a maximum tensile strength of954.18MPa. Theshock strength and toughness of rigid polyimide nanofiber are improved by addingflexible monomer. The copolyimide nanofiber has a good thermal stability,5%thermal weight loss of555.96℃and10%thermal weight loss of555.96℃. Themechanical properties and thermal stability of polyimide nanofiber are improved bychanging the ratio of MPD.