I. Definition of Organosilicon

Organosilicon, also known as organosilicon compounds, refers to compounds containing Si-C bonds, with at least one organic group directly bonded to the silicon atom. Conventionally, compounds where the organic group is connected to the silicon atom through oxygen, sulfur, nitrogen, etc., are also considered organosilicon compounds. Among these, polysiloxanes, which are composed of a silicon-oxygen bond (-Si-O-Si-) as the backbone structure, are the most numerous, most extensively studied, and most widely applied type of organosilicon compounds, accounting for over 90% of the total usage.

Organosilicon materials have a unique structure:
(1) Sufficient methyl groups on the Si atom shield the high-energy polysiloxane main chain;
(2) The non-polarity of C-H makes the intermolecular interaction force very weak;
(3) The Si-O bond is relatively long, and the Si-O-Si bond angle is large.
(4) The Si-O bond is a covalent bond with 50% ionic bond characteristics (covalent bonds have directionality, while ionic bonds do not).

II. The four major mainstream products of organosilicon are:

1. Silicone Resin

Silicone resin is a highly cross-linked network structure of polyorganosiloxane. It is usually obtained by hydrolyzing a mixture of methyltrichlorosilane, dimethyldichlorosilane, phenyltrichlorosilane, diphenyldichlorosilane, or methylphenyldichlorosilane in an organic solvent such as toluene at a lower temperature. The initial hydrolysis products are a mixture of cyclic, linear, and cross-linked polymers, usually containing a considerable amount of hydroxyl groups. After washing away the acid with water, the neutral initial condensation polymer is further condensed by thermal oxidation in air or in the presence of a catalyst, finally forming a highly cross-linked three-dimensional network structure.

Silicone resin is a thermosetting plastic. One of its most prominent properties is its excellent thermal oxidation stability. After heating at 250℃ for 24 hours, the weight loss of silicone resin is only 2～8%. Another prominent property of silicone resin is its excellent electrical insulation performance, which maintains its good insulation performance over a wide range of temperatures and frequencies.
Given the above characteristics, organosilicon resins are mainly used as insulating varnishes (including clear varnishes, porcelain varnishes, colored varnishes, impregnating varnishes, etc.) to impregnate H-class motor and transformer coils, and to impregnate glass cloth, glass fiber, and asbestos cloth to produce motor sleeves and electrical insulation windings. Large-area mica sheet insulating materials can be made by bonding mica with organosilicon insulating varnish and used as the main insulation of high-voltage motors. In addition, silicone resins can also be used as heat-resistant, weather-resistant anticorrosive coatings, metal protective coatings, waterproof and moisture-proof coatings for construction projects, mold release agents, adhesives, and can be further processed into silicone plastics. They are used in the electronics, electrical, and national defense industries as semiconductor packaging materials and insulating materials for electronic and electrical components.

Silicone resins can be broadly classified into silicone insulating varnishes, silicone coatings, silicone plastics, and silicone adhesives, based on their main applications and crosslinking methods.

2. Silicone Rubber

Silicone rubber refers to rubber whose main chain is composed of alternating silicon and oxygen atoms, with silicon atoms usually bonded to two organic groups. Ordinary silicone rubber is mainly composed of methyl-containing silicon chains and a small amount of vinyl. The introduction of phenyl can improve the high and low-temperature resistance of silicone rubber, and the introduction of trifluoropropyl and cyano can improve the temperature resistance and oil resistance of silicone rubber. Silicone rubber is one of the important products of organosilicon polymers and is widely used due to its excellent high and low-temperature resistance. Silicone rubber is mainly divided into high-temperature mixing silicone rubber and room-temperature vulcanizing silicone rubber, silicone gel, and foamed silicone rubber.
 
3. Silicone Monomer

There are many silicone products, with tens of thousands of grades and brands, and more than 5000 commonly used ones. However, its raw materials are mainly a few monomers, especially dimethyldichlorosilane, which accounts for more than 90% of all monomers. Next is phenylchlorosilane.
Silane, trimethylfluorosilane, ethyl and propylchlorosilane, vinylchlorosilane, etc. The monomer production process of organosilicon resin is complex and the process is long.
 
4. Silicone Oil

Silicone oil is a chain-like polyorganosiloxane with different degrees of polymerization. Usually, the organic groups are methyl groups, called methyl silicone oil. Common organic groups include C-based, phenyl, and hydrogen groups. Generally, silicone oil is colorless or slightly yellowish, odorless, non-toxic, and not easily volatile. It is non-corrosive. Viscosity increases with increasing molecular weight, so there are silicone oil products with different viscosities.

Silicone oil is a polyorganosiloxane with a chain-like structure of different degrees of polymerization. The most commonly used silicone oil is methyl silicone oil. Silicone oil is generally colorless (or light yellow), odorless, non-toxic, and non-volatile liquid. Silicone oil is insoluble in water, methanol, glycol, and ethoxyethanol, miscible with benzene, dimethylether, methyl ethyl ketone, carbon tetrachloride, or kerosene, and slightly soluble in acetone, dioxane, ethanol, and butanol. It has a very small vapor pressure, a high flash point and ignition point, and a low freezing point. With different numbers of segments n, the molecular weight increases and the viscosity also increases, so silicone oil can have various different viscosities. According to the chemical structure, silicone oils can be classified into methyl silicone oil, ethyl silicone oil, phenyl silicone oil, methyl hydrogen-containing silicone oil, methyl phenyl silicone oil, methyl chlorophenyl silicone oil, methyl ethoxy silicone oil, methyl trifluoropropyl silicone oil, methyl vinyl silicone oil, methyl hydroxyl silicone oil, ethyl hydrogen-containing silicone oil, hydroxyl hydrogen-containing silicone oil, cyano-containing silicone oil, etc.
Based on their uses, there are damping silicone oils, diffusion pump silicone oils, hydraulic oils, insulating oils, heat transfer oils, brake oils, etc. Silicone oils have excellent heat resistance, electrical insulation, weather resistance, hydrophobicity, physiological inertness, and low surface tension. In addition, they also have a low viscosity-temperature coefficient, high compressibility resistance, and some varieties even have radiation resistance.

Organosilicon emulsions (a form of silicone oil) mainly include silicone oil fabric softening finishing agents; silicone oil emulsion-type antifoaming agents: This is the most widely used and largest-volume antifoaming agent among organosilicon antifoaming agents.