Polymer matrices, reaction cavities with

The strategy used to design active and selective catalysts was based on the following five factors for regulation, (i) conformation of ligands coordinated to Rh atom (ii) orientation of a vacant site on Rh (iii) cavity with the template molecular shape for reaction space produced behind template removal (iv) architecture of the cavity wall and (v) micropore in inorganic polymer-matrix overlayers stabilizing the active species at the surface [46, 47, 71]. 

Structural reaction injection molding (SRIM) is usually used to produce stiff composites containing polyester or epoxy matrices. In such techniques, the mold consists of a cavity which can be subjected to vacuum. The fiber reinforcement structure in the form of mats or fabrics is placed into this cavity prior to applying vacuum, followed by injecting the two-component polymer. Vacuum, sometimes in combination with pressure, is used to introduce the polymer into the mold cavity and to force it to penetrate the fiber reinforcement structure and form the polymer matrix. For elastomer composite formation, this molding concept is new. The mold development was made because of the higher viscosity in typical two-component elastomers compared to normal polyester- or epoxy-based rigid matrix polymers. 

The first attempt to imprint a metal complex with a reaction intermediate coordinated to the metal center was reported by Mosbach and coworkers [51], A Co monomer coordinated with dibenzoylmethane, which is as an intermediate for the aldol condensation of acetophenone and benzaldehyde, was tethered to a styrene-DVB copolymer matrix. After, the template, dibenzoylmethane was removed from the polymer, the resulting molecularly imprinted cavity had a shape similar to the template due to the interaction of the template with the polymerized styrene-DVB monomers through n-n stacking and van der Waals interactions. The rate of aldol condensation of adamantyl methyl ketone and 9-acetylanthracene was lower than the rate of condensation with acetophenone, indicating some degree of increased substrate selectivity. This is the first known formation of a C-C bond using a molecularly imprinted catalytic material. 

The capture of metal complexes is achieved in the synthesis of clusters within the porous network of zeolites, where the reactants are small enough to enter the large cavities, but the clusters formed are too large to escape ( ship- in-the-bottle synthesis). The cages limit the size of the cluster compounds that can be formed and the entrance to the porous channels prevents the departure from the cages. Other methods of encapsulating metal complexes utilize polymerization or polycondensation reactions such as the sol-gel process. The metal complex is dissolved in the medium to be polymerized and is therefore trapped in the matrix formed [93] (cf. Section 3.2.2). The limitations clearly arise from the porosity of the polymer formed. A pore structure with pores that are too wide cannot prevent the leaching of the complex, whereas a pore diameter that is too small results in mass-transfer limitations. 

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