Due to the aromatic ring bonded to the polymer structure and has higher thermal stability, commercial thermoplastic polyimide derived from aromatic diamine and aromatic two anhydride. Polycondensation of aromatic polyimides prepared by aromatic diamine and aromatic usually involves two anhydride, the effect occurs in the reaction medium is suitable, and generate an intermediate polyamic acid. The polyamide acid can be used in some field or by heat or chemical action is converted into a linear thermoplastic polyimide with general structure.
The main properties of aromatic thermoplastic polyimide is high glass transition temperature (Tg) was prominent, high temperature resistance, toughness, good electrical property, flame retardancy and high natural radiation. However, since Tg and melt viscosity of thermoplastic polyimide relatively high processing temperature, a relatively high manufacturing.In some cases, the processing temperature may exceed the decomposition temperature of the polyimide. Although the processing temperature in the linear aromatic polyimide thermal decomposition temperature above theoretically is thermoplastic, but they are usually called pseudo thermoplastic polyimide. In this case, more easily than the final polyimide polyamide acid intermediate dissolve and melt, possibly before heating into polyimide becomes film or parts.Aromatic polyimide intractable problems, to a certain extent have passed in the polymer chain and resolved into such as ketone, ether and six fluorine different flexible trimethylene group or chain between two and two amine either or both of the aromatic ring. Improved thermoplastic polyimide machinability of a particularly effective aromatic diamine is perfluorinated isopropylidenebis amine (4 BDAF). 4-BDAF and aromatic two coordination reaction is shown as the figure structure of polyimide.
Easier to process than two benzene amine and aromatic two prepared polyimide polyimide from 4 to BDAF by thermal oxidation, thermal stability and still has high Tg and. 4-BDAF fluoride has also caused polyimide prepared exhibit electrical properties improved. The other is used to improve the diamine thermoplastic polyimide processing is aromatic diamine modified by siloxane and two 1 2 one or two amino benzene, indane.
The main characteristics of thermoplastic polyimide is their heat resistance, which has high Tg in them. A typical Tg scope is: from the aromatic polyether imide 423 ° F, some 4-BDAF containing polyimide exceeding 700 ° F.
Improved aromatic polyimide toughness compared with thermosetting polyimide, the elongation rate ranges from 5% to more than 50%, the fracture can range from 8.5 to 14 inch pounds per square inch.
The electrical properties of thermoplastic polyimide is excellent, and the dielectric constant of partially fluorinated aromatic polyimide from less than 2.8 (1kHz) to non fluorinated polyimide (1kHz) 3.5.
With a few exceptions, aromatic thermoplastic polyimide resistant to most common organic solvents and dilute acid. Exposure or immersed in concentrated acid alkali and heat, will make the polyimide degradation. Some thermoplastic polyimide in strong polar organic solvent is soluble in.