(1) Excellent heat resistance. The decomposition temperature of polyimide generally exceeds 500 ℃, sometimes even higher, and it is one of the known organic polymers with high thermal stability, mainly because the molecular chain contains a large number of aromatic rings.
(2) Excellent mechanical properties. The tensile strength of the unreinforced matrix material is above 100MPa. The tensile strength of Kapton film prepared with homoanhydride is 170MPa, while that of biphenyl polyimide (Upilex S) can reach 400MPa. The elastic modulus of polyimide fiber can reach 500MPa, second only to carbon fiber.
(3) Good chemical stability and heat and humidity resistance. Polyimide materials are generally insoluble in organic solvents, resistant to corrosion and hydrolysis. Varieties of different structures can be obtained by changing the molecular design. Some varieties can withstand 2 atmospheres, 120 ℃, 500h boiling.
(4) Good radiation resistance. The strength of the polyimide film remains 86% after being irradiated with a dose of 5×109rad; the strength retention rate of some polyimide fibers is 90% after being irradiated by 1×1010rad fast electrons.
(5) Good dielectric properties. The dielectric constant is less than 3.5. If fluorine atoms are introduced into the molecular chain, the dielectric constant can be reduced to about 2.5, the dielectric loss is 10, the dielectric strength is 100 to 300kV/mm, and the volume resistance is 1015-17Ω·cm. Therefore, the synthesis of fluorine-containing polyimide materials is currently a hot research field.
