Polydimethylsiloxanes (PDMS), which contain [SiMe20] repeat units, are unique among inorganic and semi-inorganic polymers. They have been the most studied members of this class by far and are the most important with regard to commercial applications. Thus, it is not surprising that a large number of reviews exist describing the synthesis, properties, and applications of these materials. The purpose of the presention however, is to focus on some novel and interesting aspects of polysiloxane history, science and engineering. The major route to produce PDMS is the Rochow process, in which ground silicon is reacted with chloromethane using a catalyst, such as copper. These compounds react with water forming dihydroxysilanes that in turn will be condensed, splitting out water, eventually forming PDMS. Historically, this high energy consumptive process has meant that siloxane production is dependent on the few companies employing the 'direct or Rochow' process. The presentation will look at what that means in today's global marketplace and the emergent new players this century. The Si-O backbone of this class of polymers endows it with a variety of intriguing properties. For example, the strength of this bond gives the siloxane polymers considerable thermal stability, which is very important for their use in high-temperature applications (for example, as heat-transfer agents and high-performance elastomers). The nature of the bonding and the chemical characteristics of typical side groups give the chains a very low surface free energy and, therefore, highly unusual and desirable surface properties. For example, polysiloxanes are often used as mold-release agents, waterproof coatings, and biomedical materials. PDMS has several unusual properties. These are listed as follows. 1. Extremely low Tg (-123 C) 2. Very high hydrophobicity 3. High thermal stability 4. Low surface tension 5. Low variation of viscosity with temperature 6. High gas permeability 7. Non-toxicity These properties have made PDMS and related polymers the most important inorganic polymers from a commercial point of view. In fact, they are the only inorganic polymers that have achieved a remarkably high level of utility and consequently are produced in large quantities throughout the world.
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