Polyimide as a promising polymer material has been fully recognized and its application in insulation and structural materials is expanding. Functional materials are emerging and their potential is still being explored. But after 40 years of development, it has not become a larger variety, mainly because the cost is still too high compared with other polymers. Therefore, one of the main research directions of polyimide in the future should be to find ways to reduce the cost of monomer synthesis and polymerization.
1. Synthesis of monomers
The monomers of polyimide are dianhydride (tetra-acid) and diamine. Synthesis methods of diamines are relatively mature, and many diamines are also commercially available. Dianhydride is a special monomer, which is mainly used for the synthesis of polyimide except as curing agent of epoxy resin. Phthalic anhydride and trimellitic anhydride can be obtained by one-step oxidation in gas phase and liquid phase from heavy aromatic oil extracted from petroleum refining products. Other and important dianhydride, if diphenylketone dianhydride, biphenyl dianhydride, diphenyl ether dianhydride, hexafluorodianhydride already was synthesized by all sorts of methods, but cost is very costly, for example every kilogram of hexafluorodianhydride achieves 10 thousand yuan. High purity 4-chlorinated anhydride and 3-chlorinated anhydride can be obtained from o-xylene chlorination, oxidation and isomerization separation developed by changchun institute of applied chemistry, Chinese academy of sciences. A series of dianhydride can be synthesized from these two compounds, which has great potential to reduce costs and is a valuable synthetic route. Foreign polyimide if the United States dupont production, there are changzhou jianbang plastic products co., ltd. and changzhou yongbang plastic industry in the production.
2. Polymerization process
The mainstream synthesis two-step and one-step polycondensation processes all use solvents with high boiling point, the price of aprotic polar solvents is higher, and it is difficult to eliminate, and finally all require high temperature treatment. PMR USES cheap alcohols. Thermoplastic polyimide can also be used in direct polymerization of diamine and anhydride in the extruder granulation, no solvent is needed, can greatly improve the efficiency. Polyimide can be synthesized by direct polymerization with diamine, bisphenol, sodium sulfide or simple sulfur without dianhydride.
3. The processing
Polyimide application is so wide, also have a variety of requirements for processing, such as high uniformity of film forming, spinning, gas phase precipitation, sub-micron lithography, etching depth straight wall, large area, big volume, ion implantation, laser precision molding processing, nanoscale hybrid technology and so on for the application of polyimide open wide heaven and earth. With the further improvement of synthetic processing technology and substantial reduction of cost, as well as superior mechanical properties and electrical insulation properties, thermoplastic polyimide is bound to play a more prominent role in the field of materials in the future. Thermoplastic polyimide is more valued for its good machinability.
4. Polyimide profile processing
Use carbide knife and cooling water to prevent stress and deformation.