Polymer support pores

New templated polymer support materials have been developed for use as re versed-phase packing materials. Pore size and particle size have not usually been precisely controlled by conventional suspension polymerization. A templated polymerization is used to obtain controllable pore size and particle-size distribution. In this technique, hydrophilic monomers and divinylbenzene are formulated and filled into pores in templated silica material, at room temperature. After polymerization, the templated silica material is removed by base hydrolysis. The surface of the polymer may be modified in various ways to obtain the desired functionality. The particles are useful in chromatography, adsorption, and ion exchange and as polymeric supports of catalysts (39,40). 

The insoluble polymer-supported Rh complexes were the first immobilized chiral catalysts.174,175 In most cases, however, the immobilization of chiral complexes caused severe reduction of the catalytic activity. Only a few investigations of possible causes have been made. The pore size of the insoluble support and the solvent may play important roles. Polymer-bound chiral Mn(III)Salen complexes were also used for asymmetric epoxidation of unfunctionalized olefins.176,177... 

As discussed in Section 1.4.2.1, the critical condensation pressure in mesopores as a function of pore radius is described by the Kelvin equation. Capillary condensation always follows after multilayer adsorption, and is therefore responsible for the second upwards trend in the S-shaped Type II or IV isotherms (Fig. 1.14). If it can be completed, i.e. all pores are filled below a relative pressure of 1, the isotherm reaches a plateau as in Type IV (mesoporous polymer support). Incomplete filling occurs with macroporous materials containing even larger pores, resulting in a Type II isotherm (macroporous polymer support), usually accompanied by a H3 hysteresis loop. Thus, the upper limit of pore size where capillary condensation can occur is determined by the vapor pressure of the adsorptive. Above this pressure, complete bulk condensation would occur. Pores greater than about 50-100 nm in diameter (macropores) cannot be measured by nitrogen adsorption. 

Another example of a macroporous methacrylate-based polymer support is shown in Fig. 1.19 [101]. Again, only the relevant pore range is displayed. The pores around 1 pm are fully revealed by mercury intrusion, whereas with nitrogen sorption, above 0.1 pm, essentially no pores can be detected. 

An investigation of the influence of surface area on the activity of the supported catalysts has shown that the activity increases with increase in surface area, but the selectivity is virtually independent of surface area (27). This result is consistent with both mechanisms i and ii. Thus, in mechanism i the reaction takes place in the pores of the catalyst, which are sufficiently large not to impose steric demands on the reactants, so that the activity of the catalyst is dependent on the rates of diffusion of the reactants to the active site. In terms of mechanism ii, in which the supported complex acts only as a precursor of a soluble catalytically active species, the activity of the catalyst will depend on the ease with which this species is abstracted from the polymer support clearly, this will increase with increasing surface area. 

Since the actual structures of the pores of the insoluble polymer supports used as gel permeation chromatography resins are not known, an exact theoretical treatment of the technique is not possible, and the gel permeation characteristics of a solute can only be compared in a relative fashion. (In alluding to molecular weights determined by this method, we shall use the term Mapp since values obtained by this method are approximate.) All estimates of polymer dimensions based on gel chromatography are therefore relative and based on those determined for polymers whose dimensions are known. 

Hi. The monomer polymerization route. Compared with the resin-functionalization route, the homo- and copolymerization of organotin-containing monomers permits one to influence the polymer resin structure to a greater extent. In principle, it is possible to prepare gel-type, macroporous, microporous or nonporous polymers. The pore structure, tin loading, solubility and other factors which influence the reactivity of the polymer-supported organotin reagents can be controlled by appropriate... 

Criteria for immobilized liquid membrane (ILM) support selection can be divided into two categories structural properties and chemical properties. Structural properties include geometry, support thickness, porosity, pore size distribution and tortuosity. Chemical criteria consist of support surface properties and reactivity of the polymer support toward fluids in contact with it. The support thickness and tortuosity determine the diffusional path length, which should be minimized. Porosity determines the volume of the liquid membrane and therefore the quantity of carrier required. The mean pore size determines the maximum pressure difference the liquid membrane can support. The support must be chemically inert toward all components in the feed phase, membrane phase, and sweep or receiving phase. 

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