Glass polysiloxane coatings

It may, therefore, be concluded that fused silica and leached glass columns coated with polysiloxanes (OV-1, 0V-101, OV-73 and SE-54) and polyethylene glycols (Superox 20M) provide... 

FIGURE 3. A schematic sketch of the polysiloxane used for rapidly curing coatings of optical glass fibers... 

For the described reason, a special structure is proposed, which is schematically shown in Fig. 23. In this figure, the structure is compared with a filled polymer structure (Si02 filled polysiloxanes, very often used as hard coatings for eye glass lenses). The figure also depicts the results of a so-called tinnble test. 

Polysiloxane deactivated capillaries - glass and fused silica - coated with Carbowax 20 M... 

The major breakthrough in the GC enantiomer separation has been the work of Bayer and associates [23,76], who synthesized a silicone-based chiral phase, stable up to 240°C. As shown in Fig. 3.14, a racemic mixture of 19 protein amino acids can be separated [23] on a glass capillary column coated with Chirasil-Val, a chiral polysiloxane phase. The phase was synthesized through coupling L-valine-tert-butylamide to a copolymer of dimethylsiloxane and carboxyalkylmethylsiloxane. 

Usually, the stationary phase including CDs in GC was prepared by depositing the modified CDs dissolved in a dimethylformamide solution onto the support (e.g. Chromosorb W) and then evaporated the solvent by vacuum heat-treatment. Some reports described glass or fused silica capillary GC column coated with peralkylated a-, P- and y-CDs dissolved in polysiloxanes. However, the coverage of CD in the surface is limited and results in limited preparative capacity [26]. In addition, the kinetics of inclusion are relatively slow and result in poor peak shape which also hinders the use of CDs as preparative phases. 

The a-, P- or y- cyclodextrins that have been permethylated must be dissolved directly in appropriate polysiloxanes mixtures, and coated on the walls of a glass or fused quartz open tubular columns. The underivatized cyclodextrins, and those that have not been permethylated, can be coated directly onto the walls of the column. Many alcohols, diols, carboxylic acids, alkanes and cycloalkanes can be separated directly on such columns without derivatization. To improve the thermal stability of the mixed stationary phase, a phenylpolysiloxane can be included in the coating material. The presence of phenylpolysiloxane can also improve its stability towards oxidation at elevated temperatures, as cyclodextrin, being basically a sugar, is very susceptible to oxidation at high temperatures. Some methysiloxane, however, must be present to increase... 

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