Macroporous-bead polymer support

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. 

The solid supports used in this study were macroporous co-polymers of vinylpyridine and styrene crosslinked with divinylbenzene. Polymers of this type in the form of beads are available commercially (e.g. Reillex 425) and were also prepared for this study by Purolite. For spectroscopic studies, a more convenient sample morphology was required and thin-film polymers of similar stoichiometry were synthesised by the group of Sherrington at the University of Strathclyde. Full details of the methods used to prepare thin film polymers are reported elsewhere.11 To generate the ion exchange resin, the pyridyl functionalities of the polymer were quatemised with methyl iodide (Eq 1). 

For example, polymer-supported CSPs with Pirkle-concept SOs (e.g. (S)-valine-3,5-dimethylaniIide) attached to monodisperse macroporous polymethaciylate beads gave reasonable enantioselectivity and efficiency for 3,5-dinitrobenzamido derivatives of a-amino acids under normal-phase conditions [368.370], It could be demonstrated that such a CSP based on polymeric particles provided enhanced enantioselectivities... 

The potential of grafted polymers remained unrecognized until the use of PS-PTFE support was resurrected in the 1990s under the phosphoramidite method [168]. The aminomethylated and loaded with nucleoside 3 -succinate from 12.5 to 48pmol per g-PS-Teflon support has been employed successfully in the automated synthesis of oligodeoxyribonucleotides as long 143-mer, with stepwise efficiency of up to 99.8%, comparing favorably with such popular carriers as silica beads CPG-500 and macroporous polystyrene Primer Support (Pharmacia). 

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]. 

The examined polymer-supported catalyst having two different granulations (bead size) A and B was the macroporous cross-linked copolymer of 4-vinylpyridine and 25% (4/1) divinylbenzene-styrene copolymer (commercial product named Reillex 425) [103]. Their average bead diameter (J), skeletal density (p), surface area ( Sbet). porc volume (Vp), and relative swelling ratio (SR) are given in Table 8.2. 

Further work demonstrated that the enzymatic route (CALB supported on macroporous beads) is viable in SCCO2, yielding PCL of Mn 12,000-37,000 g/mol with MW very similar to those obtained from the same enzymatic catalysts in organic solvents, but with lower polydispersities (typical PDI = 1.4-1.6) and higher polymer yields (typically 95-98%) [142]. 

New polymeric solid supports have been devised, which include macroporous styrene-divinylbenzene containing large fixed pores, porous glass beads, insoluble carbohydrate polymers, poly(ethylene oxide), cross-linked derivatives of polyacrylamide resins, and graft copolymers of polystyrene and poly(ethylene oxide). The last two have been the most effective and widely used and have competed well with the original copoly(styrene-divi-nylbenzene) beads. 

Macroporous and isoporous polystyrene supports have been used for onium ion catalysts in attempts to overcome intraparticle diffusional limitations on catalyst activity. A macroporous polymer may be defined as one which retains significant porosity in the dry state68-71 . The terms macroporous and macroreticular are synonomous in this review. Macroreticular is the term used by the Rohm and Haas Company to describe macroporous ion exchange resins and adsorbents 108). The terms microporous and gel have been used for cross-linked polymers which have no macropores. Both terms can be confusing. The micropores are the solvent-filled spaces between polymer chains in a swollen network. They have dimensions of one or a few molecular diameters. When swollen by solvent a macroporous polymer has both solvent-filled macropores and micropores created by the solvent within the network. A gel is defined as a solvent-swollen polymer network. It is a macroscopic solid, since it does not flow, and a microscopic liquid, since the solvent molecules and polymer chains are mobile within the network. Thus a solvent-swollen macroporous polymer is also microporous and is a gel. Non-macroporous is a better term for the polymers usually called microporous or gels. A sample of 200/400 mesh spherical non-macroporous polystyrene beads has a surface area of about 0.1 m2/g. Macroporous polystyrenes can have surface areas up to 1000 m2/g. 

An alternative method for modifying or increasing the hydrophilic balance of the resin—without the need to add a third component in the system—has been used [5—7]. In this procedure the extractant is adsorbed directly to the macroporous support after contacting the polymer with a solution of the extractant in a mixture of an organic solvent and water. Mixtures of acetone, methanol, and ethanol with water have been used. Subsequently, the polymer beads are removed from the solution by filtering, and the excess of solvent retained on the polymer is displaced by water, and the SIR is stored in water. Then, the obtained SIR is a three-component... 

Regularly macroporous ionexchange resins are prepared by suspension polymerization using water as supporting fluid. In addition to the monomer mixture a pore forming agent is included in the suspended droplets. Polymerization occurs Inside the droplets. At the end of the polymerization reaction the resin beads are removed from the water and sulfonated to creat acid groups on the polymer surface. 

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