Polysiloxanes alkyl groups

Studies of octylsilane (OS) phases, deactivated by end-capping, have shown that such stationary phases lead to a discrimination between compounds according to their H-bond donor capacity, as the stationary phase presents strong accessible H-bond acceptor groups (-Si-O-Si-) [22, 23]. For OS phases with a uniform matrix of cross-Hnked polysiloxane alkyl groups, relatively low correlations between log few and log Poet were found. 

Common chiral stationary phases for gas chromatography have cyclodextrins bonded to a conventional polysiloxane stationary phase.7-8 Cyclodextrins are naturally occurring cyclic sugars. P-Cyclodextrin has a 0.78-nm-diameter opening into a chiral, hydrophobic cavity. The hydroxyls are capped with alkyl groups to decrease the polarity of the faces.9... 

A hydrophobic tail may include such structures as straight-or branched-chain alkyl groups, long-chain alkylbenzenes, alkylnaphthalenes, perfluori-nated alkyl groups, polysiloxane groups, and others. 

The selective stationary phases were further divided in the scheme proposed by Horning et al. [79] for the steroid separations into the types selective to alcohols, ketones, multiple bonds, etc. Here, various selective interactions between the column and the separated solutes are utilized. Most importantly, various polyglycols, polyesters, polyphenyl ethers, polyamides and polyimides belong to these categories. In addition, substitution of an alkyl group in a polysiloxane polymer by a more polar... 

FIGURE 12.9 Silicone rubbers (polysiloxane). Note The alkyl group is often substituted with a variety of different groups. 

Polysiloxane n Polysiloxane is the proper name for silicones. See Polysiloxane where X and Y can be an alkyl groups. 

To reduce the inductive effect on the Si—C bond, the perfluorinated group has to be isolated from the silicon atom. Fluorination of an alkylsilane even in the P position yields hydrolytically unstable compounds which undergo thermal rearrangements and liberate Cp2=CR2- Fluorination of an alkyl group in the 7 position, CF3CH2CH2—, does not affect the Si— F bond significantly and the hydrolytic stability is adequate for practical use [132]. The dichlorosilane CF3CH2CH2Si(CH3)Cl2 hydrolyzes to form a polysiloxane. However, the ethylene link increases the bulkiness of the side chains, increases the hydrocarbon/flu-orocarbon ratio, and causes fluorocarbon-hydrocarbon and fluorine-silicone interactions and orientation effects which may reduce the surface activity of the fluorinated compound. 

Applications. Polymers with small alkyl substituents, particularly (13), are ideal candidates for elastomer formulation because of quite low temperature flexibility, hydrolytic and chemical stability, and high temperature stability. The ability to readily incorporate other substituents (in addition to methyl), particularly vinyl groups, should provide for conventional cure sites. In light of the biocompatibility of polysiloxanes and P—O- and P—N-substituted polyphosphazenes, poly(alkyl/arylphosphazenes) are also likely to be biocompatible polymers. Therefore, biomedical applications can also be envisaged for (3). A third potential application is in the area of solid-state batteries. The first steps toward ionic conductivity have been observed with polymers (13) and (15) using lithium and silver salts (78). 

---