Polyimide High Insulating Properties

Polyimide (abbreviated as PI) refers to a class of polymers containing imide rings (-CO-N-CO-) in the main chain, and is one of the organic polymer materials with the best comprehensive properties. Its high temperature resistance is above 400 °C, the long-term use temperature range is -200 ~ 300 °C, some parts have no obvious melting point, high insulation performance, dielectric constant 4.0 at 103 Hz, dielectric loss is only 0.004 ~ 0.007, belongs to F to H class insulation.

According to the chemical structure of the repeating unit, polyimides can be divided into three types: aliphatic, semi-aromatic and aromatic polyimides. According to the interaction force between chains, it can be divided into cross-linked and non-cross-linked.

As a special engineering material, polyimide has been widely used in aviation, aerospace, microelectronics, nano, liquid crystal, separation membrane, laser and other fields. In the 1960s, all countries listed the research, development and utilization of polyimide as one of the most promising engineering plastics in the 21st century. Polyimide, because of its outstanding characteristics in performance and synthesis, whether as a structural material or as a functional material, its huge application prospects have been fully recognized, and it is known as a "problem-solving expert" ( problem solver), and believed that "there would be no microelectronics technology today without polyimide".

Polyimide has a wide variety of forms and forms, and there are many ways to synthesize it, so it can be selected according to various application purposes. This flexibility in synthesis is also difficult for other polymers to have. The synthesis is introduced as follows:

Polyimide is mainly synthesized from dibasic anhydride and dibasic amine, these two monomers are combined with many other heterocyclic polymers, such as polybenzimidazole, polybenzimidazole, polybenzothiazole, polyquinoline and other monomers In comparison, the source of raw materials is wide and the synthesis is relatively easy. There are many kinds of dianhydrides and diamines, and different combinations can obtain polyimides with different properties.

Polyimide can be polycondensed at low temperature from dianhydride and diamine in polar solvents, such as DMF, DMAC, NMP or THE/methanol mixed solvent, to obtain soluble polyamic acid. Dehydration at about 300 ° C to form a ring into a polyimide; acetic anhydride and a tertiary amine catalyst can also be added to the polyamic acid for chemical dehydration and cyclization to obtain a polyimide solution and powder. Diamines and dianhydrides can also be polycondensed by heating in high-boiling solvents, such as phenolic solvents, to obtain polyimide in one step. In addition, polyimide can also be obtained from the reaction of dibasic ester of tetrabasic acid and dibasic amine; it can also be transformed from polyamic acid into polyisoimide first, and then into polyimide. These methods all bring convenience to processing. The former is called PMR method, which can obtain low-viscosity, high-solid solutions. There is a window with low melt viscosity during processing, which is especially suitable for the manufacture of composite materials; the latter increases the In order to improve the solubility, no low-molecular-weight compounds are released during the conversion process.