Siloxanes phenyl-modified

Phenyl and vinyl modified versions of poly(m-carborane-siloxane) were readily prepared using the procedure just described, by introducing the appropriate silane feed into the reaction mix.19 Typically, 1 to 3 mol % di-chloro-methylvinylsilane was added to the di-chlorosilane feed in the syntheses described earlier. The repeat unit of the phenyl modified poly(w-carborane-siloxane) is shown in 5. 

The phenyl modified polymers show a significant decrease In weight loss compared to their all methyl analog (6). In a study of the thermal breakdown of phenyl substituted carborane-slloxane polymers, It has been reported that the presence of phenyl groups In carborane-siloxanes leads to cross-linking and less loss of weight ( ) ... 

The most commonly used siloxane modifiers are those having phenyl, trifluoro-propyl and cyanopropyl substituents. Introduction of phenyl units into the polydimethylsiloxane backbone either in the form of methylphenylsiloxane or diphenyl-siloxane increases the thermal and oxidative stability, glass transition temperature and the organic solubility characteristics of the resulting copolymers. At low levels (5-10 percent by weight) of incorporation, bulky phenyl groups also break up the regularity of polydimethylsiloxane chains and inhibit the crystallization (Tc... 

Several other stationary phases made from different proportions of typical phases (methyl, phenyl, cyanopropyl), or from special compounds such as polytrifluropropyl-siloxane, or different columns such as PLOT (porous layer open tubular), columns coated with a modified graphitized carbon or with a silicone based polymer with chiral groups incorporated into the polymeric chain, columns coated with derivatized cyclodextrins (for the separation of chiral compounds), etc. are also utilized. 

Chiral WCOT columns suitable for the enantiomeric separation of small molecules such as esters, ketones, alkanes and alcohols have recently been introduced. One example of a chiral column has a stationary phase film consisting of a non-bonded mid-polar, 35% phenyl 65% methyl siloxane modified by embedding in the film permethylated a- or /3-cyclodextrin. Elution characteristics are modified by the cyclodextrin content DEX 110 contains 10% cyclodextrin and DEX 120, 20% [127, 128]. 

As an alternative to the two-step approach, mesoporous silica with organic moieties covalently linked to their internal surface could be obtained in a single-step cocondensation of siloxane and organosiloxane precursors using similar supramolecular templating techniques as those for the synthesis of pure silica. Successful one-step syntheses of MCM-41 silicas modified with alkyl, phenyl, vinyl. cyanoethyL amine, thiol, and propylsulfonic acid moieties were reported in the literature.Similar preparations were extended to MCM-48 silica and to meso-... 

The liquid stationary phases used with capillary columns are similar to those used in packed columns. The most common stationary phases are polysiloxanes (silicones) that contain various substituents that modify the polarity of the phase. Polydimethyl siloxane (methyl silicone) is nonpolar. Replacing methyl groups with increasing numbers of phenyl substituents increases the polarity of the silicone. For example, J W DB-1, or a similar stationary phase sold by other companies, has the same properties as methyl silicone (SE-30 or DC-200) and is used with nonpolar... 

The functionalities in those phases are the methyl, phenyl, cyano, trifluoro, and hydroxy-ether group, respectively. The similarity with HPLC phases is remarkable. Based on the above, Sandra et al. [22] proposed five basic phases for capillary GC. The formulas are given in Figure 12. For the majority of high-resolution separations, these stationary phases provide more than adequate performance. For some applications, the functionalities are combined on the same siloxane backbone, or columns are coupled (selectivity tuning). Functionalities can also be modified to provide specific interactions. Optical phases and liquid crystals complete the set of preferred CGC phases. These tailor-made phases are discussed in Section ] 1.3.4.3.3. 

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