Porous reaction sites control

The benefits refer to the ability to achieve defined thin, highly porous coatings in micro reactors. In combination with the small length scales of the channels, diffusion to the active sites is facilitated. The residence time can be controlled, accurately minimizing consecutive reactions which may reduce selectivity. 

Functionalized polymers are of interest in a variety of applications including but not limited to fire retardants, selective sorption resins, chromatography media, controlled release devices and phase transfer catalysts. This research has been conducted in an effort to functionalize a polymer with a variety of different reactive sites for use in membrane applications. These membranes are to be used for the specific separation and removal of metal ions of interest. A porous support was used to obtain membranes of a specified thickness with the desired mechanical stability. The monomer employed in this study was vinylbenzyl chloride, and it was lightly crosslinked with divinylbenzene in a photopolymerization. Specific ligands incorporated into the membrane film include dimethyl phosphonate esters, isopropyl phosphonate esters, phosphonic acid, and triethyl ammonium chloride groups. Most of the functionalization reactions were conducted with the solid membrane and liquid reactants, however, the vinylbenzyl chloride monomer was transformed to vinylbenzyl triethyl ammonium chloride prior to polymerization in some cases. The reaction conditions and analysis tools for uniformly derivatizing the crosslinked vinylbenzyl chloride / divinyl benzene films are presented in detail. 

Shape selective reactions are typically carried out over zeolites, molecular sieves and other porous materials. There are three major classifications of shape selectivity including (1) reactant shape selectivity where reactants of sizes less than the pore size of the support are allowed to enter the pores to react over active sites, (2) product shape selectivity where products of sizes smaller than the pore dimensions can leave the catalyst and (3) transition state shape selectivity where sizes of pores can influence the types of transition states that may form. Other materials like porphyrins, vesicles, micelles, cryptands and cage complexes have been shown to control product selectivities by shape selective processes. 

For this reason, recent attention has been dedicated to micro- and meso-porous materials (MMM), and also for their possible use as shape-selectivity controlled reactions (space-restricted transition states, preferential diffusion and back-diffusion). Even if the latter aspects are better known regarding the performances of microporous materials, other aspects can be evidenced. In fact, also in mesoporous materials, where the dimensions of the channels are larger, as required for shape-selectivity effects, a change of reactivity of molecules inside the channels could be present due to confinement effects [281]. Therefore, the catalytic reactivity shown by basic sites located inside mesoporous channels could differ from that of the same sites located instead on the external surface of the mesoporous ordered material. 

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