Mesoporous polymeric networks

Self-assembled polymeric structures have promising applications in nanomaterials synthesis. As demonstrated by Zhou and Lodge for bicontinuous microemulsions of poly-isoprene/polystyrene [9], mesoporous polymeric networks (Fig. 7.4) can be obtained by... 

Figure 7.4 Freeze-fracture SEM micrograph mesoporous polymeric networks obtained by sulphur monochloride cross-linking of polyisoprene in bicontinuous polymeric microemulsions of polyisoprene and polystyrene. (From Ref. [9], reprinted with permission of the American Chemical Society.)...

FIGURE 1.7 Influence of the polymerization time on the porosity of monolithic MS/BVPE polymer networks, determined by MIP. Reduction of the polymerization time converts a narrow monomodal pore distribution into a broad bimodal distribution, comprising mesopores. 

Ordered mesoporous polymers have been produced by filling with divinylbenzene, ethyleneglycol dimethacrylate, or a mixture of the two the pores of a colloidal crystal are formed by silica spheres of 35 nm of diameter. Thereafter, the polymerization and subsequent dissolution of the silica template leave a polycrystalline network of interconnected pores [235],... 

A key factor in the development of adsorption technology for the fluid separation has been the availability of appropriate adsorbents. The most frequently used categories include crystalline materials like zeolites, and amorphous materials like activated carbons, silica and alumina gels, polymeric sorbents, and ion-exchange resins. These materials exhibit a large spectrum of pore structures (networks of micro- and mesopores of different shapes and sizes) and surface chemistry (degrees of polarity), which provide a large choice of core adsorptive properties (equilibria, kinetics, and heat) to be utilized in... 

The microporous alumino-silicate zeolites (Types A, X, and mordenite are frequently used) provide a variety of pore openings (3-10 A), cavity and channel sizes, and framework Si/Al ratios. They are also available in various cationic exchanged forms (Na, K, Li, Ag, Ca, Ba, Mg), which govern their pore openings and cationic adsorption site polarities. They are highly hydrophilic materials and must be dehydrated before use. The amorphous adsorbents contain an intricate network of micropores and mesopores of various shapes and sizes. The pore size distribution may vary over a wide range. The activated carbons and the polymeric sorbents are relatively hydrophobic in nature. The silica and alumina gels are more hydrophilic (less than zeolites) and they must also be dehydrated before use. 

The OMC structure also depends on the polymerization step. As mentioned above, the polymerization of the precursor adsorbed in the pore system of the matrix is catalyzed by acids. Different synthesis procedures were developed. For example, an acid solution can be added to the reaction mixture. In this case, the polymerization will take place throughout the entire pore system of the matrix. The resulting OMC can be described as a three-dimensional network of interconnected carbon rods. An example is CMK-3, already presented in Fig. 18.1. In this OMC, parallel-arranged carbon rods with a diameter of approximately 5 nm are connected by narrower carbon rods. The narrow carbon rods were formed in micropores that connect the mesopores of the SBA-15 silica matrix [21]. In an alternative synthesis procedure, a matrix with acid sites on the pore walls (e.g., an aluminosilicate) can be used. In this case, the polymerization of the precursor takes place on the mesopore walls and a carbon film is formed there, whereas the much narrower micropores are entirely filled with the polymerization product. Thus, after pyrolysis and removal of the matrix, the OMC consists of interconnected nanopipes, as opposed to interconnected carbon rods. An example is CMK-5. This OMC is synthesized in an acid form of the matrix used for the synthesis of CMK-3. Thus, CMK-5 consists of interconnected carbon nanopipes, arranged in the same fashion as the carbon rods of CMK-3 (Fig. 18.2) [22]. However, the pore system of these two OMCs differs. The pore system of CMK-3 consists of the voids in between the carbon rods, whereas in addition to these pores CMK-5 also has pores inside the nanopipes. 

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