History

The first aromatic polyimides were created by Marston Bogert in 1908 ^[1]. High molecular weight aromatic polyimides were created in 1955 by polycondensing pyromellitic dianhydride with diamines thrice ^[2]. DuPont's laboratories and relevant research facilities in the former Soviet Union reported the creation of polyimide fibers in the 1960s ^[3]. Shanghai Synthetic Fiber Research Institute in China also established a pioneering position in the fabrication of small-batch polyimide fibers for use in cable coatings and radiation-protection ropes. Polyimide fiber did not, however, develop on a big scale as quickly as other high-performance polymer fibers (aramid fiber, PBO fiber, etc.) because of the high cost of raw materials and the immaturity of synthesis and spinning technologies. Eventually, the Rhone Poulenc France firm created poly (amide-imide) fiber, which was later marketed under the brand name Kermel®, as depicted in Fig. 1 ^[4].

Figure 1. Structures of Kermel® and P84® fibers ^[5].

The first PEI that is used for commercial purposes was patented by General Electric Co. in 1975 and later purchased by SABIC. It is marketed under the name Ultem. Frazier et al. examined photosensitive polyimide and plasma etching techniques for the creation of metallic microstructures in 1994 ^[6]. Frazier talked about the sensing uses of composite materials made of graphite and polyimide in 1995 ^[7]. The processing methods of polyimides, including wet etching, dry etching, photopatterning, and laser ablation processes, were covered in an engineering study of new materials for microscale sensors and actuators in 2007 ^[8]. In their 2016 assessment of the advancement of polymer micromachining technology, Kim and Meng briefly explored polyimide microfabrication techniques ^[9].

Figure 2. Domestic PI film localization process

Long literature review

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