First, the performance of silicone
The basic structural unit (that is, the main chain) of silicone products is composed of silicon-oxygen chains, and the side chains are connected to various other organic groups through silicon atoms. Therefore, the structure of silicone products 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. It has many excellent properties such as high and low temperature resistance, weathering resistance, electrical insulation, ozone resistance, hydrophobicity, flame retardant, non-toxic, non-corrosive and physiological inertness. Some varieties also have oil resistance, solvent resistance and radiation resistance. Compared with other polymer materials, the most outstanding properties of silicone products are excellent temperature resistance, dielectric properties, weather resistance, physiological inertness and low surface tension.
1. Temperature resistance
Most of the general polymer materials are based on carbon-carbon (C-C) bonds as the main chain structure, such as plastics, rubber, chemical fibers, etc., while silicone products are based on silicon-oxygen (Si-O) bonds as the main chain. In terms of structure, the bond energy of the C-C bond is 82.6 kcal/mol, and the bond energy of the Si-O bond is 121 kcal/mol in the silicone, so the thermal stability of the silicone product is high, under high temperature ( or radiation exposure) the chemical bonds of the molecules are not broken or decomposed. Silicone is not only resistant to high temperatures, but also low temperatures, and can be used in a wide temperature range. Whether it is chemical properties or physical and mechanical properties, the change with temperature is very small, which is also related to the flexible helical structure of silicone molecules.
2. Weather resistance
The main chain of silicone products is -Si-O-, and there is no double bond, so it is not easy to be decomposed by ultraviolet light and ozone. In silicone products, the chain length of the Si-O bond is approximately one and a half times the chain length of the C-C bond. Longer chain lengths give silicones better thermal stability and resistance to radiation and weather than other polymer materials. The service life of silicone in natural environment can reach several decades.
3. 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.
4. physiological inertia
Polysiloxanes are among the most inactive compounds known. They are very resistant to biological aging, have no rejection reaction with animal bodies, and have good anticoagulant properties.
5. Low surface tension and low surface energy
The backbone of silicone is very flexible, and this excellent flexibility is due to the basic geometric molecular configuration. Because its intermolecular force is much weaker than that of hydrocarbons, it has lower viscosity, weaker surface tension, smaller 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.
Second, the classification of silicone
Silicone is mainly divided into four categories: silicone oil, silicone rubber, silicone resin and silane coupling agent.
Third, the use of silicone
Due to these excellent properties of silicone, it has a very wide range of applications. It is not only used as a special material in aviation, cutting-edge technology, and military technology departments, but also in various sectors of the national economy. Metal and paint, medicine and medical, etc.
The main applications of silicone oil and its derivatives are: release agent, shock absorption oil, dielectric oil, hydraulic oil, heat transfer oil, diffusion pump oil, defoamer, lubricant, hydrophobic agent, paint additive, polishing agent, cosmetics And daily necessities additives, surfactants, particle and fiber treatment agents, silicone grease, flocculants.
Silicone rubber is divided into room temperature vulcanization silicone rubber and high temperature vulcanization silicone rubber. The former is mainly used in: sealants, adhesives, conformal coatings, gaskets, foam rubber, molded parts, packaging materials, electrical insulation, glazing, medical implants, surgical aids, molding materials; the latter Mainly used in: pipes and hoses, strips, wire and cable insulation materials, surgical aids, flame retardant rubber parts, penetration sealing materials, molded parts, embossed rollers, automotive ignition cables and spark plug covers, extruded parts , medical implants, laminates, conductive rubber, fiber coatings, foam rubber.
The main applications of silicone resins are: varnishes, insulating varnishes, molding compounds, protective coatings, encapsulation materials, joint coatings, pressure sensitive adhesives, laminating resins, release agents, adhesives, masonry waterproofing agents.
Silane coupling agents are mainly used in paints, plastics and rubber processing, and adhesives.
Silicone can not only be used as a basic material and structural material in some large industries, but also can be used as an auxiliary or auxiliary material to share with other materials or improve the process performance of other materials.
4. Silicone monomer
The raw materials for preparing silicone oil, silicone rubber, silicone resin and silane coupling agent are various organosilicon monomers, and thousands of organosilicon products can be produced from several basic monomers. Organosilicon monomers mainly include: methylchlorosilane (referred to as methyl monomer), phenylchlorosilane (referred to as phenyl monomer), methylvinylchlorosilane, ethyltrichlorosilane, propyltrichlorosilane, Vinyl trichlorosilane, γ-chloropropyl trichlorosilane and fluorosilicon monomers, etc. Among them, methylchlorosilane is the most important, and its dosage accounts for more than 90% of the total monomer, followed by phenylchlorosilane.
The key to the development of any polymer material lies in the development of monomer technology. The silicone industry is characterized by centralized monomer production and decentralized product processing. Therefore, monomer production occupies an important position in the silicone industry, and the production level of monomer directly reflects the development level of the silicone industry.
5. Silicone polymer
1. polyorganosiloxane
Polyorganosiloxane is the most important silicone polymer, and most of the silicone products on the market today belong to this form. Chain polyorganosiloxane with unit structure R2SiO, often referred to as silicone.
Polyorganosiloxanes can be roughly divided into long-chain structures and complex cross-linked structures. Silicone oil and silicone rubber belong to the former, and silicone paint belongs to the latter. In addition, polyorganosiloxane can also be classified according to the organic groups on silicon, in most cases can be called methyl polyorganosiloxane (unit structure Me2SiO), phenyl polyorganosiloxane (unit Structure Ph2SiO, PhSiO3/2) and hydrogen-containing polyorganosiloxane (unit structure MeHSiO) and so on.
2. Polyorganoalkane(ar)siloxane
A polymer containing a phenylene (alkylene) group in a siloxane segment has a thermal stability higher than that of polydimethylsiloxane by 100°C or more, which is of special significance.
3. polysiloxane
4. polysilazane
5. Silicon-containing carbon-based polymers in pendant groups
6. Polysilane
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