Macroporous beads

Column sorbents for aqueous media show )ust average properties. This is due to the different copolymerization process, which does not allow easy formation of macroporous beads with proper pore topology. This fact also reflects many experiences of SEC users, who have to input much more effort to get good aqueous SEC work accomplished. 

The developed method reduced the number of steps required for the synthesis of uniform macroporous beads since the larger uniform seed latices were prepared by the dispersion polymerization relative to those obtained... 

In addition, it has been shown that other enzymes such as trypsin can be successfully immobilized and used for the conversion of substrates with higher molecular masses [76]. Petro et al. [94] compared the activity of trypsin immobilized on macroporous beads and on monolithic supports. They were able to show that the catalytic activity of trypsin bound to a monolith was much higher and resulted in a much higher throughput. Other enzymes such as invertase [76] and... 

The pore size distributions of the molded monoliths are quite different from those observed for classical macroporous beads. An example of pore size distribution curves is shown in Fig. 3. An extensive study of the types of pores obtained during polymerization both in suspension and in an unstirred mold has revealed that, in contrast to common wisdom, there are some important differences between the suspension polymerization used for the preparation of beads and the bulk-like polymerization process utilized for the preparation of molded monoliths. In the case of polymerization in an unstirred mold the most important differences are the lack of interfacial tension between the aqueous and organic phases, and the absence of dynamic forces that are typical of stirred dispersions [60]. 

Note 3 The location of active sites introduced into a polymer support depends on the type of polymer support. In a swollen-gel-bead polymer support the active sites are distributed uniformly throughout the beads, whereas in a macroporous-bead polymer support they are predominantly on the internal surfaces of the macropores. 

Later, Howdle and coworkers supported lipase CA on macroporous beads... 

Increasing the amount of cross-linking agent (divinyl compound) at expense of monomer causes a decrease in pore size, which is accompanied by a distinct increase in surface area [101-104]. Even if this has been observed for macroporous beads prepared by suspension polymerization, the results can directly be transferred to the fabrication of rigid monolithic materials in an unstirred mold by thermally [105,106] as well as photochemically [107] initiated free radical copolymerization. 

Ion-exchange resins are produced as gelular resins, which are homogeneous cross-linked polymers, or macroporous beads which have pores produced with a porogen, to allow ion transport [113,119],... 

The first type of polymer we studied was macroporous polystyrene beads functionalised with potassium sulphonate groups.17 Macroporous beads were used because they are particularly easily to separate. The functionalised beads were used to "fish" in a pool of commercial crown ethers. Whilst some of the crown ethers bound to the beads, unfortunately it appeared that many were just simply adsorbed. The second type of polymer studied, in an otherwise similar system, was gel-type beads. These have no inner surfaces for adsorbtion. However, even here adsorbtion appeared to be a problem.17 It was concluded from these early studies that it would be better to use a soluble polymer as the "fishing rod". 

Synthesis routes are reviewed for preparation of polymers from styrene, divinylbenzene (and possibly functionalized monomers) to give membranes, gel-form beads, and macroporous beads. Methods are summarized for functionalization of these polymers to give pendent groups such as -Br and -CH2CI, which can be converted into ligands such as -PPI12, -NR2>... 

If nonporous, the beads are transparent.) Physical properties of the macroporous beads are reported in Table I. 

Model for macroporous beads where diffusion in both the gel-phase and the macropores is comparable. 

X Fritz and X N. Story, Selectivity behavior low[Pg.57]

The diameter of these spherical macroporous beads was 2 to A mm, the pore... 

Figure 2. (a) Macroporous polymer beads synthesized using scCOs as the porogen (entry 4, Table 1) (b) Variation in BET surface area of macroporous beads as a Junction of CO2 pressure. 

The most extensively used macroporous resins are polystyrene-based ion-exchange resins. They are made of poly(styrene-co-divinylbenzene) with subsequent modification to arylsulphonic acids, quaternary ammonium salts or other derivatives mainly located on the internal surface of the pores [33,34]. This renders them accessible to munerous organic solvents including water and alcohols. Recently, these ion-exchange resins have had a revival for the immo-biUsation of ionic reagents [31,32] in automated synthesis. Macroporous beads have also been used for the immobihsation of catalysts [5,7] however, leach-... 

Two different catalysts for hydrogen peroxide decomposition, the enzyme peroxidase (isolated from the horseradish root, HRP), and polymer-supported catalyst (acid form of poly-4-vinylpyri-dine functionalized by ferric sulfate, apFe) [99,100], are examined with an aim to compare their activity. The active center in the peroxidases is the ferric ion in protoporphyrin IX. Besides the complex made of ferric ion and protoporphyrin IX, that is ferricprotoporphyrin IX, also known as ferric heme or hemin, peroxidase possesses a long chain of proteins [101,102]. On the other hand, the macroporous acid form of polyvinyl pyridine functionalized by ferricsulfate is obtained from cross-linked polyvinyl pyridine in macroporous bead form [103]. Pyridine enables it to form coordination complexes or quaternary salts with different metal ions such as iron (111) [104]. An active center on the polymeric matrix functionalized by iron, as metallic catalyst immobilized on polymer by pyridine, has similar microenvironment conditions as active center in an enzyme [105]. 

Complications of hydroquinone therapy include acute and chronic reactions. Common acute reactions are irritant and allergic contact dermatitis, and postinflammatory hyperpigmentation. Lesional and perile-sional hypopigmentation may occur. This is usually a temporary complication. With repeated application, hydroquinone may cause destruction of melanosomes, melanocyte organelles, and melanocyte necrosis [32]. A novel formulation of hydroquinone 4% plus retinol 0.15%, in which most of the hydroquinone and all of the retinol are encapsulated into macroporous beads, allows gradual delivery of hydroquinone into the skin, minimizing the effects of skin irritation [34-36]... 

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