Since the second half of the 19th century, the only insulating materials suitable for high voltage were ceramics and glass when erecting power transmission lines. In the 1940s, due to the advent of polymer materials, ceramics and glass are no longer the preferred insulator materials. European and American countries began to study polymer insulators. Then the physical properties, electrical properties, long-term reliability and optimal shape of the electrical insulator are studied, and the productivity has been continuously improved.

Among the polymer materials that can replace ceramics and glass, silicone rubber has had practical achievements since the 1960s and stands out among several polymers. Silicon rubber insulator has more advantages than ceramic insulator. First, it is light, easy to operate and safe; In addition, ceramic insulators often suffer from breakage, and they will be damaged under impact. The silicone rubber insulator can resist mechanical impact such as vehicle collision with pole.

Although other polymer materials also have the advantages described above, only silicone rubber will not cause too much pollution to the environment. The polymer insulator is waterproof, so there will be no leakage and surface arc due to water drops. The waterproof property of silicone rubber insulator recovers faster than that of other polymer insulators. It is a durable material that can be used for a long time in harsh environments.

The main chain of silicone rubber is composed of siloxane (Si-O) chain. Since the negative electricity of Si and O on this bond is 1.8 and 3.5 respectively, which are very different, the polarization structure shown in Fig. 1 (omitted) is formed, which has the property of ionic bond. In this way, the bond energy of Si-O is higher than that of C-C (see Table 1). In addition, ① due to the property of the main chain ionic bond, the ionic property of the side chain methyl C-H is weakened, and it is not easy to be attacked by other molecules, so its chemical stability is good; ② Since Si does not form double bond and triple bond, it is difficult to form the starting point of main chain decomposition (Si-C bond is quite stable for this reason), which leads to more stable main chain of silicone rubber.