Silicone oil, generally refers to a linear polysiloxane product that remains in a liquid state at room temperature. The structural formula is shown in Figure 1, and Figure 2 is a simulated formula.






Figure 1 Structural formula of linear polysiloxane


  
Figure 2 Simulation of silicone oil
It is widely used in our life and production. The most common applications are in medical, cosmetic, lubricating oil, working oil, anti-vibration oil, heat carrier and so on.


Figure 3 Some applications of silicone oil
Commercially available silicone oils can be classified into four categories according to their structure: hydrocarbon-based silicone oils, silicon-functional silicone oils, carbon-functional silicone oils, and inactive modified silicone oils. Here we only talk about hydrocarbon-based silicone oil, dimethyl silicone oil is one of the main representatives of hydrocarbon-based silicone oil, so take dimethyl silicone oil as an example, and listen to Xiaobian slowly.
Dimethicone (ie, R, R' and X are methyl) is the most widely used and widely used variety of silicone oils. It has typical polysiloxane properties such as high, low temperature, oxidation resistance and viscosity. Low temperature coefficient, shear resistance, low vapor pressure, low surface tension, hydrophobicity, defoaming, demoulding, electrical insulation and physiological inertia.
The main chain and branch of linear and branched silicone oils are composed of Si-O-Si, and the terminal groups and side groups are all hydrocarbon groups (such as methyl, ethyl, etc.), so they can be made from corresponding monomers or intermediates. take.


Figure 4 Molecular formula of dimethicone
Industrially, dimethyl silicone oil is mainly produced by four methods:
(1) Co-hydrolysis condensation method of MeSiCl2 and Me3SiCl;




Figure 5 Hydrolysis condensation method
The raw materials used in the method (1) are the cheapest, but the process is complicated, the corrosion is severe, and the purity of the monomer is high, and even if it contains little impurities, the product performance can be seriously affected. Therefore, it is not practical.
(2) MeSiCl2 hydrolysate (ie a mixture of (Me2SiO)n and HO(Me2SiO)nH) and MM or Me3SiO(Me2SiO)2-5SiMe3 catalytic equilibrium method;


Figure 6 Reaction (2) equation
(3) (Me2SiO)n and MM or Me3SiO(Me2SiO)2-5SiMe3 catalytic equilibrium method;


Figure 7 Reaction (3) equation
(4) HO(Me2SiO)nH and MM or Me3SiO(Me2SiO)1-5SiMe3 catalytic polycondensation method.




Figure 8 Reaction (4) equation
Among the above reactions, (2), (3), and (4) (i.e., the siloxane catalytic equilibrium method) are more practical. Therefore, most of the latter three methods are used in industrial production.
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