Porogens

A porous polystyrene-divinylbenzene gel is produced by suspension polymerization in an aqueous system with incorporation of more than 5 mol% initiator to a total amount of styrene and divinylbenzene with an inert organic solvent as diluent and porogen (24). 

A process for the preparation of porous polyvinyl alcohol gels in three steps is (1) suspension polymerization of vinyl acetate with diethylene glycol dimethacrylate in the presence of a diluent as porogen, (2) saponifying of the resulting porous polyvinyl acetate gel with an alkali, and then (3) subjecting... 

The second step in the production of monodispersed polymer particles involves the swelling of activated particles with a monomer or a mixture of monomers, diluents, and porogens, and the shape of the swollen oil droplets must be maintained in the continuous aqueous phase. The monomer or the mixture of monomers may be added in bulk form, preferably as an aqueous dispersion to increase the rate of swelling, especially in the case of relatively water-insoluble monomers. 

Monodispersed poly (methyl methacrylate-ethyleneglycol dimethacrylate) is prepared by a multistep swelling and polymerization method. When a good solvent such as toluene is applied as a porogen, the seed polymer severely affects the pore structure, whereas no effects are observed with poor solvents, such as cyclohexanol, as a porogen, in comparison with the conventional suspension polymerization (68,69). 

In the multistep swelling and polymerization method, polymerization time, temperature, and initiator concentration have marginal effects only. The ratio of monovinyl to divinyl monomer in the polymerization mixture, along with the composition of the porogenic systems, is known to be the most important factor in controlling the ultimate macroporous structure. The average molecular... 

The effects of the concentration of divinylbenzene on pore-size distribution and surface areas of micropores, mesopores, and macropores in monosized PS-DVB beads prepared in the presence of linear polymeric porogens have been studied (65). While the total surface area is clearly determined by the content of divinylbenzene, the sum of pore volumes for mesoforms and macropores, as well as their pore-size distribution, do not change within a broad range of DVB concentrations. However, the more cross-linked the beads, the better the mechanical and hydrodynamic properties. 

Fig. 6-10. Influence of the number of basic interaction sites of the template versus the separation factor measured in chromatography for the corresponding racemate. The templates were imprinted using MAA as functional monomer by thermochemical initiation at 60/90/120 °C (24 h at each temperature) and using acetonitrile as porogen. (From Sellergren et al. [15].)...

Other microporous materials have been synthesized using the porogen polyethylene glycol in polyethylene oxide-urethane gels [27]. Micropores were formed in the gel, and it was found that the diffusion of larger species, vitamin B12, was enhanced relatively more than that of a smaller species, proxyphylline. This result is in qualitative agreement with that found for electrophoretic transport by RiU et al. [322] discussed earher, where the mobility of larger species was preferentially enhanced in the templated media. 

Badiger, MV McNeill, ME Graham, NB, Porogens in the Preparation of Microporous Hydrogels based on Poly(ethylene oxides). Biomaterials 14,1059, 1993. 

Figure 2. Representative optical micrographs of poly-HEMA cross-linked with EDMA. (a) and (b) represent the gel-type polymer produced by suspension co-polymerization in the dry and swollen state, respectively, (c) and (d) represent the macroreticular polymer produced by suspension co-polymerization in the presence of a porogen (toluene), in the dry and swollen (vide infra) state, respeetively [13], (Reprinted from Ref [15], 1996, with permission from Elsevier.)...

It is of much interest to compare polymer monoliths with monolithic silica columns for practical purposes of column selection. Methacrylate-based polymer monoliths have been evaluated extensively in comparison with silica monoliths (Moravcova et al., 2004). The methacrylate-based capillary columns were prepared from butyl methacrylate, ethylene dimethacrylate, in a porogenic mixture of water, 1-propanol, and 1,4-butanediol, and compared with commercial silica particulate and monolithic columns (Chromolith Performance). 

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