Silicon-oxygen backbone

Moisture-Curing Silicones. The formulation of moisture-curing silicones includes a silicone polymer, filler, a moisture-reactive cross-linker, and sometimes a catalyst. The most common silicone polymer used in sealant formulations is an alternating silicon—oxygen backbone with methyl groups attached to the silicon such as the silicone polymer (1). 

Fluorosilicones can be compounded by the addition of mineral fillers and pigments. Fillers for such compounds are most commonly silicas (silicon dioxide), because they are compatible with the elastomeric silicon-oxygen backbone and thermally very stable. They range in surface areas from 0.54 to 400 m2/g and average particle size from 100 to 6 nm. Because of these properties, they offer a great deal of flexibility in reinforcement. Thus, cured compounds can have Durometer A hardness from 40 to 80. Other fillers commonly used in fluorosilicones are calcium carbonate, titanium dioxide, and zinc oxide. 

Definition Family of syn. polymers contg. a repeating silicon-oxygen backbone with org. side groups attached via carbon-silicon bonds classified as fluids, resins, and elastomers Formula [—OSiR2—]n, R not equal to H Properties Liq., semisolid, or solid cis 1 to >1,000,000 cs water repellent sol. in most organic solvents... 

One big area where silicones have found their way into technical products with a wide range of applications is silicone rubbers. The first products were introduced into the market in the 1950s [1]. This was possible due to the unique prop es of silicones (also known as polysiloxanes) based on their molecular structure with a silicon/oxygen backbone, where the remaining valences of the silicon atom are saturated by hydrocarbon radicals (mainly methyl groups). Both silicones and silicone rubbers exhibit outstanding properties such as ... 

Chemistry. The silicone polymer chain is based on an alternating silicon-oxygen backbone. SR coatings are available in three types, room temperature vulcanizing (RTV), UV cure, and catalyzing (addition) cure. 

Silicones. SiHcoae fluids coasist of an alternating siHcon—oxygen backbone (sdoxane), with two organic side groups branching off from each of the siHcon atoms. Although there are many possibiHties, methyl and phenyl side chains have been the most common (46,47). 

Silicones are probably best known for their application as sealants and as release materials for pressure sensitive adhesives [107]. The silicone polymer combines an inorganic backbone made from silicon-oxygen bonds with organic substitution on the silicon atom. This repeating unit, shown below is called a siloxane. 

Silicon oxychloride, in fiber optic fabrication, 11 138 Silicon-oxygen (Si-O) backbone, in moisture-curing silicones, 22 32... 

Silicones. Polydimethylsiloxanes, polydiphenylsiloxanes, and polymethylphenylsiloxanes are generally called silicones (see Silicon COMPOUNDS, silicones). With a repeating unit of alternating silicon—oxygen, the siloxane chemical backbone structure, silicone possesses excellent thermal stability and... 

Note that polymers with a simple silicone-type backbone, i.e., with a backbone consisting solely of alternating silicon and oxygen atoms, such as poly(dimethyl siloxane) (Figure 5.2) and poly[oxy(methylphenylsilylene)] (Figure 6.11), have two Si-O backbone bonds per repeat unit. 

A large variety of aluminum and silicon polymers with metal oxygen backbones have been made besides the poly(siloxanes). Poly(aluminosiloxanes) contain an Si-O-Al-0 backbone. A typical example results from the reaction of sodium salts of dimethylsiloxane oligomers with aluminum chloride. Polymers with Si/Al ratios of 0.8 to 23 have been made. Low Si/Al ratios are brittle and insoluble having a 3-dimensional structure while those with Si/Al ratios of 7 to 23 are soluble. 

Polymer Preparation. In order to prepare silicon containing polymers which include the m-xylyl and dimethylenebiphenyl moieties, two distinct polymerization routes were chosen. The first route consists of condensation of a dichlorodialkyl(or aryl)silane with a dicarbanion, namely 12 or 12. The material which is formed consists of an all silicon-carbon and carbon-carbon backbone. The second polymerization utilizes the bis(silanol) monomers discussed in the previous section. These materials are heated and undergo a self condensation reaction to form polymers which contain silicon-carbon, silicon-oxygen, and carbon-carbon bonds in the backbone. 

The silicone-oxygen bond has one of the highest torsional mobilities in any polymer backbone, e.g., Tg of polyfmethyl siloxane) is -130 °C. Polydimethylsiloxane (-[Si(CH3)20] -) is more stable to thermooxidative attack than is the aliphatic C-O bond but is sensitive to certain reagents such as acids and bases. 

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