Polymer-modified glasses, silica-type

If the hydrolyses in silane precursor-polymer systems are carried out using relatively large amounts of the silane, then the silica generated can become the continuous phase, with the elastomeric polysiloxane dispersed in it.12 14 136-143 Again, a variety of ceramic components and polymeric components have been studied. The resultant composite is a polymer-modified glass or ceramic, frequently of very good transparency. Although its thermal stability will be inferior to that of the ceramic component itself, there are many applications for ceramic-type materials where this is not a serious problem. 

The photoiniferter polymerization has been used for the modification of various surfaces including polymeric films, gold, silica, glass and silicone surfaces. Although, this technique is limited for microchannels, tubes, or small cavities, which are very difficult to modify and have very limited light accessibility, it provides a versatile route to 2D- and 3D-microstructured polymer brushes with various types of monomers. Table 3.6 summarizes the surfaces, conditions and polymers obtained by surface initiated photoiniferter polymerization. 

Pellicular or controlled surface porosity particles were introduced in the late 1960s these have a solid inert impervious spherical core with a thin outer layer of interactive stationary phase, 1-2 pm thick [13]. Originally, the inner sphere was a glass bead, 35-50 pm i.d., with a thin active polymer film or a layer of sintered modified silica particles on its surface. Such particles were not very stable, had very low sample load capacities because of low surface areas and are not used any more. Nowadays, this type of material is available as micropellicular silica or polymer-based particles of size 1.5 to 2.5 pm [14]. Micropellicular particles are usually packed in short columns and because of fast mass-transfer kinetics have outstanding efficiency for the separation of macromolecules. Because the solutes are eluted as very sharp narrow peaks, such columns require a chromatograph designed to minimise the extra-column contributions to band broadening. 

Solid-liquid extraction by use of sorbents (silica, alkyIsllane-modified silica, alumina, porous polymers with or without ion-exchange groups or carbon materials) contained in a cartridge or a short stainless-steel or glass column is the pretreatment most commonly used at present for some types of samples... 

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