Starting from the second half of the 19th century, the only insulation materials suitable for high voltage during the installation of transmission lines were ceramics and glass. In the 1940s, due to the emergence of polymer materials, ceramics and glass were no longer the preferred insulation materials, and European and American countries began to research polymer insulators. Subsequently, research was conducted on the physical and electrical properties, long-term reliability, and optimal shape of electrical insulators, and the productivity was continuously improved.

Among the polymer materials that can replace ceramics and glass, silicone rubber has had practical performance since the 1960s, standing out among several polymers. Silicone rubber insulators have more advantages than ceramic insulators. Firstly, it is lightweight, easy to operate, and safe; In addition, ceramic insulators often suffer from breakage, which can cause damage under one impact. Silicone rubber insulators can resist mechanical shock such as vehicle collision with poles.

Although other polymer materials also have the advantages introduced above, only silicone rubber will not cause significant environmental pollution. Polymer insulators can be waterproof, so there will be no leakage or surface arc caused by water droplets falling. The waterproof performance of silicone rubber insulators recovers faster than other polymer insulators, making them a durable material that can be used for a long time in harsh environments.

Characteristics of silicone rubber:
The main chain of silicone rubber is composed of siloxane (Si O) chains. Due to the significant differences in the negative charges of Si and O on this bond, which are 1.8 and 3.5 respectively, it exhibits ionic bonding properties. In this way, the bond energy of Si-O is higher than that of C-C (see Table 1). In addition, ① the ionic properties of side chain methyl C-H are weakened due to the properties of the main chain ionic bond, so it is not easy to be attacked by other molecules, so its chemical stability is good; ② Due to the fact that Si does not form double or triple bonds, it is difficult to form a starting point for the decomposition of the main chain (due to this reason, the Si-C bond is quite stable), resulting in a more stable main chain of silicone rubber.

Characteristics of silicone rubber:
Heat and cold resistance; Waterproof performance; Electrical performance; Weather resistance; Permanent deformation

Classification of silicone rubber:
According to the characteristics before vulcanization, silicone rubber can be divided into solid and liquid, and can also be divided into peroxide vulcanization, addition reaction vulcanization and condensation reaction vulcanization according to the vulcanization mechanism. The difference between solid and liquid silicone rubber lies in the molecular weight of polysiloxane. Solid silicone rubber can be vulcanized by any one of peroxide vulcanization and addition reaction, commonly referred to as high-temperature vulcanized rubber (HTV) and thermal vulcanized rubber (HCR). Although liquid silicone rubber materials cured by addition reaction can also be cured at room temperature, they are called liquid silicone rubber (LSR), low temperature vulcanized rubber (LTV) and two-component room temperature vulcanized rubber (RTV) due to different molding methods and curing temperatures. When manufacturing polymer insulators, injection molding and pouring molding methods are usually used.