Phenyl silicone properties

Modification of the properties of the phenyl silicones is possible through chlorination of the aromatic nucleus.43 One or more chlorine atoms may be substituted for hydrogen in each ring, as by chlorination of the phenylchlorosilane with iron powder as a carrier. The chloro-phenylchlorosilane is then hydrolyzed, and the resulting silicols are condensed by heat, just as is done with unsubstituted phenylchloro-silanes. The product is a brittle fusible resin, but it melts at a higher temperature than phenyl silicone and is less flammable. If an average of three chlorine atoms has been introduced into each phenyl nucleus, the product will not bum at all. 

Ethyl phenyl silicone is another alkyl-aryl silicone which may be made either from ethylphenyldichlorosilane41 or by cocondensation of mixed ethyl and phenyl chlorosilanes. The cross-linked ethyl phenyl silicone resins have good dielectric and mechanical properties, but their maximum service temperatures in air are somewhat lower than those for methyl phenyl silicone, being limited to about 250° C. for... 

When is a small number, the structure is that of a silicone oil, whereas silicon rubbers have high values of . when the ratio R/Si is lower than 2, cross-linked polymers are obtained. Properties of silicone polymers are greatly affected by the type of organic radical present. For a given chain length, a methyl silicone can be an oily liquid, but a phenyl silicone is a hard and brittle resin. 

In these elastomers, 5—15% of the methyl groups of polydimethylsiloxane are replaced by phenyl groups to give materials with especially good low temperature properties. The relatively large phenyl groups reduce intermolecular forces and retard the tendency of the polymer to stiffen as the temperature is lowered. Thus dimethyl silicone elastomers lose their elasticity at about —50°C whereas phenyl silicones retain their elasticity at temperatures as low as —lOO C. 

Table 2.10 Typical highlighting properties of high-methyl and high-phenyl silicone resins...

Matching density is less difficult with a horizontal bath. The sample merely must be less dense than the fluid. Typically, dimethyl and phenyl silicone oils and perfluorinated polyethers are used for higher density. Clearly the oil must not diffuse into the sample. A sensitive test for diffusion is actually to watch for changes with time in rheological properties like ijq. Other techniques such as infrared have been used (Munstedt, 1979). 

The replacement of 5-10% of the methyl groups on the silicon atom with phenyl groups gives polymers which exhibit superior low temperature properties. Brittleness temperatures of approximately -117 °C can be achieved compared to the approximately -70 °C for the VMQ types. The ISO designation for the phenyl modified silicones is either PMQ or PVMQ depending on whether the grade is vinyl modified. 

Backer, M. W. Pernisz, U. C. Photoexcitation and Photoemission Spectra of Phenyl-Substituted Cyclosiloxanes. In Synthesis and Properties of Silicones and Silicone-Modified Materials Clarson, S. J., Fitzgerald, J. J., Owen, M. J., Smith, S. D., Van Dyke, M. E., Eds. ACS Symposium Series 838 American Chemical Society Washington, DC, 2003 pp 105-116. 

Gas chromatographic analysis of the product (Hewlett-Packard fused silica, cross-linked methyl silicone capillary column, 25 m x 20 mm, column temperature 100-270°C, injection temperature 250°C) shows that the product is over 99% chemically and isomerically pure, (Z,E)-l-Phenyl-l,3-octadiene shows the following spectral properties IR (neat) cm 1640, 1595, 1490, 985 ... 

The thermal stability, as well as structure-related properties, such as resistivity and elasticity, of polysiloxanes is dependent on the nature of the pendant groups on the silicon atoms. Thus high-molecular-weight polydimethylsiloxanes are attacked at temperatures near 200 °C in the presence of oxygen, but substitution of a phenyl group for one methyl group raises the oxidative stability to 225 °C. 

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