Reports about polyimide polymers can be traced back to before the First World War. Unfortunately, people did not know much about it at that time, so polyimide did not receive much attention. It was not until around 1960 that companies represented by DuPont in the United States developed a series of polyimide materials and sold them in the market, and the value of polyimide was gradually known. In recent years, with the vigorous development of aerospace, microelectronics, nano, liquid crystal, laser and other technologies, the application prospects of polyimide are also becoming more and more extensive. Now, polyimide has been recognized by various countries as “one of the promising engineering plastics in the 21st century”.
Polyimide (sometimes abbreviated as “PI”) refers to a class of polymers containing imide rings (-CO-N-CO-) in the main chain. 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 type and non-cross-linked type.
As one of the organic polymer materials with good comprehensive properties, polyimide has the following properties:
● High temperature resistance up to 400℃, long-term use temperature range is -200℃～300℃
● Extremely low temperature resistance, no embrittlement in liquid helium at -269℃
● Excellent insulating properties, the dielectric constant is 4.0 at 10 3 Hz, and the dielectric loss is only 0.004 to 0.007, belonging to F to H class insulating materials
● Excellent mechanical properties, the tensile strength of unfilled plastics is above 100Mpa
● Self-extinguishing, low smoke rate
● Non-toxic and can withstand thousands of sterilizations
● Some polyimide varieties are insoluble in organic solvents and stable to dilute acid, while general varieties are not very resistant to hydrolysis
● According to thermogravimetric analysis, the decomposition temperature of fully aromatic polyimide is generally around 500℃; the thermal decomposition temperature of polyimide synthesized from pyromellitic dianhydride and p-phenylenediamine reaches 600℃, which is One of the most thermally stable varieties of polymers so far.
Film is one of the earliest commodities of polyimide, mainly used for H-class insulation, such as cable insulation materials, heat insulation materials, radiation protection materials, recording carrier materials, etc.
Polyimide is found in many detectors and space telescopes in space.