The basic structural unit of organic silica gel is composed of silicon-oxygen chains, and the side chains are connected with various other organic groups through silicon atoms. Therefore, the structure of the silicone coating material contains both "organic groups" and "inorganic structures". This special composition and molecular structure make it integrate the characteristics of organic matter and the function of inorganic matter. The outstanding properties of silicone products are:

1.1 High temperature resistance
Since the molecular structure of organic silicon has structural characteristics similar to inorganic polymers, its bond energy is very high, so it has excellent heat resistance. The use temperature of rubber-type silicone is about 250℃, and the resin-type silicone can be used for a long time at 350℃.

1.2 Low temperature resistance
Rubber-type silicone has long bonds, large bond angles, and is very soft. Its glass transition temperature is generally around -123°C, and it can be used for a long time in the range of -5O~250°C. Special products can be used within -100~300°C, such as silicone rubber containing 7.5 (molar content) phenyl. Remains elastic at -112°C.

1.3 Weather resistance
There are no double bonds in the main chain of organic silica gel, so it is not easy to be decomposed by ultraviolet light and ozone. Long-term exposure to outdoor or high ozone concentration environment will not cause cracking and viscous creep, and the physical and electrical properties are basically unchanged. Resin-based silicone will not turn yellow even under intense ultraviolet irradiation, and its color will remain unchanged for many years.

1.4 Hydrophobicity
In the organic silica gel, the methyl group is connected to the silicon atom by a bond, which increases the space for free rotation, and the hydrogen atoms on the outwardly arranged methyl groups repel each other with the hydrogen atoms of the water, making it difficult for the water molecules to interact with the hydrophilicity. The oxygen is close to it, so it has strong hydrophobicity. Methyl hydrogen polysiloxane or polyethyl hydrogen siloxane containing Si-H bond has reactivity and strong orientation, and can be cross-linked by catalyst at low temperature to form a hydrophobic film.

1.5 Breathability
Because the polysiloxane molecule has a helical structure and a large free space, the silicone rubber coating film has good gas and vapor permeability, such as the permeability of nitrogen, oxygen, carbon dioxide and other gases in the air at room temperature. The rate is 30 to 50 times higher than that of natural rubber, and it is selective. Therefore, it has been widely used in separation membranes of gas and water vapor, artificial heart-lung machines, oxygen-enriched devices, etc.

1.6 Low surface tension and low surface energy
The main chain of silicone is very flexible, and its intermolecular force is much weaker than that of hydrocarbons. Therefore, it has lower viscosity, weaker surface tension, lower surface energy, and stronger film-forming ability than hydrocarbons of the same molecular weight. This low surface tension and low surface energy are the main reasons for its many applications: hydrophobicity, defoaming, foam stabilization, anti-sticking, lubrication, glazing and other excellent properties.

1.7 Electrical insulation properties
Silicone products have good electrical insulation properties, and their dielectric loss, withstand voltage, arc resistance, corona resistance, volume resistivity and surface resistivity are among the best in insulating materials, and their electrical properties are affected by temperature and frequency. impact is small. Therefore, they are a stable electrical insulating material and are widely used in the electronics and electrical industries. In addition to excellent heat resistance, silicone also has excellent water repellency, which is the guarantee of high reliability of electrical equipment in wet conditions.

1.8 Physiologically inert (non-toxic)
With the correct selection of reliable cross-linking and catalytic systems, silicone elastomers are fully cross-linked and non-toxic and harmless, and can be used in the food and medical industries.

To sum up, because organic silica gel has many excellent physical and chemical properties, it can be used in many occasions and environments, and will play an important role in more fields. In the next period of time, organic silica gel will achieve rapid development in the following aspects.

(1) Improvement of curing methods: from traditional thermal curing to radiation curing and microwave curing. At present, important progress has been made in UV-curable silicone release agents and optical fiber coatings.

(2) Introduction of functional groups: replacing the commonly used methyl and phenyl groups with amino groups, epoxy groups, allyl groups, and hydroxyl groups can change the physical properties and chemical reactivity of organic silica gels in a wide range.

(3) Composite use with other materials: Although silicone has many excellent properties, it also has disadvantages such as low strength and poor adhesion to the substrate. The modification of the copolymerization method can achieve the effect of complementary performance.