Silicones - Properties and Applications
A World of Unlimited Possibilities
We encounter silicones every day without noticing them. Beneath the engine hood Silicone rubbers protect car electronics against moisture and dirt Silicone Resin Emulsion Paints ensure masonry remains water-repellent but also permeable for water vapor and carbon dioxide in its interior. But also in medical applications, in which high resistance is necessary, or where cutting edge products are required, silicones produce genuine peak performance – as particularly pure material in medical tubes, wound dressings or orthopedic products, and as safe sealing and insulating materials in electrical equipment or insulators.
From Science to Success
About 75 years ago, the Müller-Rochow process was developed, allowing methylchlorosilane to be obtained from silicon and methyl chloride. This step provided the starting materials for the industrial manufacturing of silicones and started the global boom in the use of silicone products in many different applications. WACKER is a pioneer in this field, and was the first company in Europe to begin researching silicones. In the following years, WACKER processes laid the cornerstone for the modern and efficient manufacturing of organochlorosilanes and silicone products.
This was the beginning of the success story. These early scientific accomplishments underlie WACKER’s reputation as the European pioneer of silicone chemistry. Now, in complex chemical processes, the globally active WACKER Group develops, produces and markets a versatile product portfolio.
The backbone of silicones is based on an Si-O bond, whose stability significantly exceeds that of the C-C bonds of organic compounds. This has far-reaching effects on the stability and resistance of silicones to a variety of influences. For example, silicones have remarkable thermal and thermooxidative
resistance. They also have reduced sensitivity to electromagnetic or particle radiation (UV, alpha, beta and gamma radiation) compared to organic plastics.
A Versatile Formula
Silicones’ chemical structure allows them to be produced in a number of variations. By using siloxane units with different functionalities, products can be made with oily,
polymeric, resinous or rubbery properties. At the same time, the organic groups bound to the silicon pave the way for a diverse range of modifications. It is this variability that makes possible the impressive variety of silicone products: greases, release agents, antifoam agents, paint additives, paper coatings, hydrophobizing agents, high or room-temperature vulcanizing silicone rubbers, and many, many more.
Silanes are the Starting Point
The starting point and chief building blocks for silicone production are silanes. Silanes are produced by direct synthesis from silicon and methyl chloride (Müller Rochow synthesis). They are found as colorless, water-white, low-viscosity liquids that are soluble in organic solvents. The low molecular mass of silanes makes them highly volatile.
Structure of Silicones
Silicones, known to chemists as polydimethylsiloxanes, have a structure that resembles quartz modified with organic groups. They consist of an “inorganic” backbone built up of alternating silicon and oxygen atoms. The other two bonds of the silicon atoms are occupied with organic groups (preferably methyls), which are responsible for silicones’ exceptional chemical characteristics.
The Term “Silicone”
The term “silicone” was coined by F. S. Kipping (1863-1949), and refers to the formal analogy between these silicon compounds and the equivalent oxygen compounds of carbon
(polysilicoketones). However, the Si-O-Si group is better described by the term “siloxane.” Strictly speaking, therefore, all silicones should correctly be termed “polysiloxanes.” Nowadays, the term silicone is principally used in conjunction with the technical applications of polysiloxanes.