Macropores, monoliths

Although much remains to be done in the study of macroporous monoliths, recent achievements open new vistas for the preparation of supports and separation media with exactly tailored properties. The experimental work done so far... 

Monolithic columns with the chiral anion exchange-type selectors incorporated into the polymer matrix obtained through in situ copolymerization process of a chiral monomer (in situ approach) [80-83,85] or attached to the surface of a reactive monolith in a subsequent derivatization step (postmodification strategy) [84], both turned out to be viable routes to enantioselective macroporous monolithic columns devoid of the limitations of packed columns mentioned earlier. 

Lammerhofer, M., Tobler, E., Zarbl, E., Lindner, W., Svec, E, and Frechet, J. M. J. (2003). Macroporous monolithic chiral stationary phases for capillary electrochromatography new chiral monomer derived from cinchona alkaloid with enhanced enantioselectivity. Electrophoresis 24, 2986-2999. 

The polymerization mixture for the preparation of rigid, macroporous monolithic materials in an unstirred mold generally contains a monovinyl compound (monomer), a divinyl compound (crosslinker), an inert diluent (porogen), as well as an initiator. The mechanism of pore formation of such a mixture has been postulated by Seidl et al. [101], Guyot and Bartholin [102], and Kun and Kunin [103] and can be summarized as in the following text. 

Fig. 10.16. Gradient electrochromatogram of derivatized neutral steroids. Macroporous monolithic column 350 (250) mm x 100 pm i.d. gradient mobile phase, acetonitrile-water-240 mM ammonium formate buffer, pH 3 (30 60 5-65 30 5 v/v/v) field strength, 600 V/cm injection, 100 V/cm for 10s detection, laser-induced fluorescence (excitation at 325 nm, emission at >495 nm). Reproduced with permission from Que et al. [76],...

Fig. 11. a SEM image of an ordered macroporous monolith, formed by assembling PS spheres coated with five silicalite nanoparticle/polyelectrolyte layer pairs into a close-packed arrangement, and subsequently calcining, b TEM image of the silicalite framework in a. c Corresponding diffraction pattern. (Adapted from [42], by permission of the American Chemical Society)... 

The free radical polymerisation of commercial divinylbenzene led to a crosslinked macroporous monolith. The overall interconnected open-cellular macrostructure of the material can be clearly seen by scanning electron microscopy (fig.l). 

Macroporous monolith, amino (normal phase) Macroporous monolith, C12 (reverse phase) [216]... 

Aerojet has made organic aerogels with densities of 0.1-0.2 g/mL3 for use in insulators and capacitors.252 Transparent macroporous monoliths have also been made by polymerization of trimethylolpropanetrimethacrylate using toluene, ethyl formate, and other liquids as poro-gens.253 Poly(alkyl methacrylates) have good resistance to outdoor weathering and can be used in windows. 

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