As promising polyimide polymer material has been fully recognized, applications in insulation and structural materials is constantly expanding. In terms of functional materials although there have been a lot of material to get used, but its potential is still excavations. Polyimide After half a century of development has not yet become a greater variety is mainly due to higher costs. But from chemical point of view, the cost of polyimide is lowered. There are two ways to reduce costs: First, in the polymerization process to find ways monomer synthesis; Second polyimides other polymers to improve performance in order to develop a new class of performance is slightly lower than the aromatic polyimides, but higher than the new breed was modified polymers.
（1）Synthesis of monomers: polyimide monomer is a dianhydride (D acid) and diamine. Diamine synthesis method is relatively mature, there are also many diamine supply of goods. Dianhydride monomer is rather special, in addition to use as a curing agent for epoxy resin are mainly used for polyimide synthesis. Pyromellitic dianhydride and trimellitic anhydride can be refined petroleum products and the weight of durene partial three toluene vapor and liquid phase oxidation step to obtain an aromatic oil raised. Other important dianhydride, benzophenone dianhydride, biphenyl dianhydride, diphenyl ether dianhydride, hexafluoro dianhydride synthesized by various methods, but the cost is very expensive. Such as hexafluoro dianhydride few thousand dollars per thousand Dakota. Chinese Academy of Changchun Institute of Applied Chemistry developed by o-xylene chlorination, oxidation and then by separation of isomers can be obtained high purity 4-chloro-3-chloro anhydride and phthalic anhydride. In these two series of compounds as raw materials can be synthesized dianhydride, its great potential for cost reduction is a valuable synthetic route.
(2) Polymerization process: currently used in two-step, one-step polycondensation process uses a high-boiling solvent, aprotic polar solvents higher price, it is difficult divisible, eventually requires high temperature processing. PMR method using cheap alcohol solvent. You can also use a thermoplastic polyimide dianhydride and a diamine polymerized directly in an extruder and pelletized, the solvent is no longer needed, can greatly improve efficiency. Chlorophthalic anhydride without the dianhydride and diamine diclofenac first bisimide, and then in various ways directly polymerized to obtain a polyimide, is a very economical synthetic route.
(3) Polyimide polymer make other high performance: Copolymerization, blending polyimide and nylon, polyester, polycarbonate, and epoxy resins combined with a lot of work has been published in the article. Such modified polymers, although there are some varieties of applications received, but still far from reaching the required level, its potential is still very bright prospects.
In addition to the cost-related problems in recent years for the study of heterogeneous polyimide increasing cause for concern, such polymers have called the "second generation of polyimide." Because the positional isomers dianhydride and a diamine of the resultant polyimide comparison with the conventional polyimide having a higher glass transition temperature, lower melt viscosity, while maintaining the high thermal oxidative stability, excellent mechanical and electrical insulation properties. Some also have a tendency to form isomers macrocycle. Research in this area is only in the beginning, I believe that regardless of all will achieve greater progress in research on synthetic or performance, particularly in terms of the potential for functional materials are far from understanding. Can expect from heterogeneous polyimide will develop more new polymer materials.
Indeed, polyimides are still many problems to solve, such as the development can be a low temperature (such as room temperature ~ 200 ℃) curing, high temperature (300 ℃ above) structure and curing method used, zero birefringent film material with high thermal conductivity materials and other functional materials.
We always believe that with a significant reduction in synthesis technology and further improve the processing technology and cost, has excellent overall performance polyimide will occupy a more prominent position in the field of future materials.