Dimethyl silicone oil (Polydimethylsiloxane, PDMS for short) is the most basic and widely used organosilicon polymer, with polydimethylsiloxane as the main chain and -(CH₃)₂SiO- as the repeating unit in the molecular structure. It combines the stability of inorganic silicon and the flexibility of organic compounds, and is the core basic material of the organosilicon industry. It is a colorless, transparent, odorless and tasteless liquid at room temperature, and its viscosity can be flexibly adjusted according to the degree of polymerization (10~10⁶ mPa·s). Relying on excellent high and low temperature resistance, hydrophobicity, electrical insulation and chemical inertness, it has become an indispensable functional material in industrial manufacturing, daily chemicals, medical care and other fields. Its synthesis process and performance control technology directly determine the application upper limit of downstream products.
The core advantage of dimethyl silicone oil stems from its unique molecular structure. The bond energy of the Si-O main chain is as high as 452 kJ/mol, much higher than that of the C-C bond, endowing it with excellent high and low temperature resistance. It can maintain stability in a wide temperature range of -50℃~200℃, does not decompose or volatilize at high temperatures, and does not solidify or become brittle at low temperatures. The symmetrical distribution of methyl side chains gives it extremely low surface tension (20~21 mN/m), excellent lubricity, hydrophobicity and mold release properties; at the same time, the weak intermolecular forces endow it with good fluidity and defoaming properties, and strong chemical inertness, which does not react with most acids, alkalis and organic solvents, adapting to various complex working conditions.
At present, the mainstream synthesis process of dimethyl silicone oil is alkali-catalyzed equilibrium polymerization. The core raw materials are dimethyl cyclosiloxane mixture (DMC, mainly containing D3, D4, D5) and end-capping agent (such as hexamethyldisiloxane). Under the action of alkali catalysts such as potassium hydroxide and tetramethylammonium hydroxide, the finished product is obtained through ring-opening polymerization, equilibrium reaction, neutralization, removal of low-boiling substances, precision filtration and other processes. This process has the advantages of simple operation, low cost and mature large-scale production, and is the main method of industrial production at present, with a reaction conversion rate of more than 99%.
Performance control and process upgrading focus on precise viscosity control and purity improvement. By optimizing the raw material ratio, reaction temperature and time, the degree of polymerization can be precisely controlled to realize the customized production of products with different viscosities, adapting to the diversified needs from mold release agents to high-end lubrication; the low-boiling removal process is improved, and vacuum distillation combined with membrane separation technology is used to remove light component impurities and unreacted monomers, improving the product purity to more than 99.9%, reducing volatile components, and meeting the strict requirements of medical, food contact and other harsh scenarios. In addition, the promotion of solvent-free synthesis processes reduces VOC emissions, conforms to the development trend of green chemical industry, and promotes the upgrading of dimethyl silicone oil from general-purpose to high-end customized type.