Synthesis Of Polyimide In Polyphosphoric Acid And Analysis Of Structures And Properties Of Its Fiber

Poly(imide-benzoxazole)(PIBO) fiber and poly(imide-benzimidazole)(PIBI) fiber exhibit high mechanical properties, excellent thermal stability and superior chemical resistance, besides these, they also have good electrical properties and dimension stability. As a kind of special type of material for engineering, it is used in such areas as aviation, space flight, microelectronics, nanometer, liquid crystal, diffusion barrier and laser, and it is one of the materials which are used most widely among aromatic polyamide fibers with thermal stability at present."Two-step"method was used in this paper to synthesize two kinds of polyimide(PI), which contain benzoxazole and benzimidazole respectively. First of all, benzoxazole-diamine and benzimidazole-diamine were synthesized in polyphosphoric acid(PPA), whose compositions were characterized with FT-IR and elemental analysis.Poly(imide-benazole) was characterized by means of FT-IR and thermo gravimetric analysis. The effect of concentration of P2O5 and temperature of reaction to the inherent viscosity of poly(imide-benazole) was researched. The best techniques of polymerization under the condition of this experiment was selected, that was under the condition of the protecting atmosphere of N2, temperature of reaction was controlled between 180 and 200℃, the concentration of P2O5 in PPA was 84-85%, the speed of stirring was controlled at about 250-300 r/min. Thermo gravimetric analysis showed that the thermal decomposing temperature of polymer prepared was to 615℃for PIBI and up to 620℃for PIBO, which had good thermal stability.The solution of poly(imide-benzimidazole)(PIBI) in PPA was used for a spinning dope, fiber of PIBI was prepared by dry-jet wet spinning. The solution of Poly(imide-benzoxazole)(PIBO) in PPA was used for a spinning dope, fiber of PIBO was prepared by dry-jet wet spinning. Images of SEM were used to analyze the fiber surface of the two kinds of PIs, and it has been showed that the surfaces of PIBI and PIBO were smooth. The mechanical property of the fiber of PIBI could reach 2.1GPa; while that of PIBO could achieve 2.4GPa.