According to its physical properties, it can be divided into crystalline amorphous. Most polyimides are amorphous, only a few structures are crystalline semi-crystalline. The crystalline type has an obvious melting point a lower melt viscosity. Mechanical. Above the melting point. It is the type of structure developed for thermoplastic polyimide. Amorphous polyimide has no melting point its glass transition temperature (Tg) is higher than the melt viscosity, which is still very high, is generally used for molding.
According to chemical characteristics, it can be divided into thermoplastics thermosetting plastics. Thermoplastics can be heated melted like ordinary plastics, can be injected, extruded, molded, such as PI100 series, PI200 series, YS20, Kaw, etc. Thermosetting refers to materials that contain double bonds acetylene groups, similar to materials such as unsaturated resins epoxy resins, which require high temperature heating to be cured molded, such as bismaleimide (BMI), polystyrene-containing end groups Special examples of main uses: PMDA+ODA structure polyimide plastic has no obvious processing melting point, can be processed with thermoplastic materials, nor can it be processed with ordinary thermosetting materials, but processed by high temperature high pressure methods. powder metallurgy. In fact, experts generally think that the structure of materials can be defined as the third category: non-plastic polyimide.
1. According to thermogravimetric analysis of fully aromatic polyimide, the decomposition temperature is generally around 500℃. The polyimide synthesized biphenyltetracarboxylic dianhydride p-phenylenediamine has a thermal decomposition temperature of 600°C is one of the high thermal stability varieties of polymers so far.
2. Polyimide can withstand extremely low temperatures, such as brittle cracked in liquid helium at -269°C.
3. Polyimide has excellent mechanical properties. The tensile strength of unfilled plastics is more than 100Mpa, the Kapton film (Kapton) is more than 170Mpa. Hangzhou Plastics Thermoplastic Polyimide (TPI) The impact strength is as high as 261KJ/m2. The biphenyl polyimide (Upilex S) reaches 400Mpa. As an engineering plastic, the amount of elastic film is usually 3-4 Gpa, the fiber can reach 200 Gpa. According to theoretical calculations, the fiber synthesized by pyromellitic dianhydride p-phenylenediamine can reach 500 Gpa, second only to carbon fiber.
4. Some polyimide varieties are insoluble in organic solvents stable to dilute acids. The general varieties are resistant to hydrolysis. This seemingly shortcoming performance makes polyimide a big difference other high-performance polymers. The characteristic of this is that the raw materials dianhydride diamine can be recovered by alkaline hydrolysis. For example, for Kapton film, the recovery rate can reach 80%-90%. Changing the structure can also produce varieties that are quite resistant to hydrolysis, such as those that can withstand boiling at 120°C for 500 hours.