Macroporous polymer beads suspension polymerization

The syndiesis of macroporous polymer beads by suspension polymerization using scCOa as a pressure-adjustable porogen. 

Washington, D.C., 2001, p.125-6. 012 SYNTHESIS OF MACROPOROUS POLYMER BEADS BY SUSPENSION POLYMERIZATION USING SUPERCRITICAL CARBON DIOXIDE AS A PRESSURE-ADJUSTABLE POROGEN Wood C D Cooper AI Liverpool,University... 

Macroporous polymer beads, synthesized by suspension polymerization, are a class of polymer beads containing a permanent, well-developed porous structure in a dry state and having a wide range of applications—such as support for catalysts, immobilization of enzymes, HPLC columns, liberation of active substances, or adsorbents. 

Particle Size and Shape. The polymerization process for producing macroporous synthetic polymers (539) leads to the formation of spherical particles whose size can be controlled within certain limits. The popular XAD polymers are usually sold with approximately 90 of the total weight encompassing smooth beads with 20-50-mesh sizes. Most users incorporate a suspension step to remove the fines in their purification of the polymer, but they do not remove the small number of particles larger than 20 mesh. The particle size and distribution vary with different polymer batches, and it is advisable to mechanically sieve polymer beads and choose only those within the 20-50-mesh size for preparation of the adsorption columns. 

Macroporous Polymers Prepared by Suspension Polymerization. Unlike the non-porous "glass beads", all macroporous polymers prepared by suspension polymerization with toluene as cosolvent exhibit fluoresence emission that parallels the solvent correlation line (Figure 2). This finding indicates a substantial degree of probe solvation. Indeed, even the 501 crosslinked material (DVB-5O-S-T), exhibits solvation behavior similar to the lightly crosslinked 5 glass beads. An Important difference in this series occurs in the poor swelling solvents (EtOH). In this solvent the 5 and 20 crosslinked materials (DVB-5-S-T, DVB-20-S-T) exhibit a fluoresence emission that parallels the "dry" polymer, however, the emission of 50 crosslinked material (DVB-50-S-T) remains close to the pure... 

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. 

The most common supports are insoluble particles of polystyrenes (PS), cross-linked with divinylbenzene (DVB), and silica gel (SG). Soluble polymers have been used as supports and separated by precipitation or by ultrafiltration. Insoluble PS beads are prepared by suspension polymerization. They can be either microporous or macroporous (synonymous with macroretic-ular). " Typical average particle diameters are 50 gm for peptide synthesis and 500 jum for ion exchange. PS beads are used in the form of solvent-swollen gels. The micropores are created by solvent, and removal of solvent collapses the pores. A macroporous polymer retains pores in the dry state and may have as much as 700 m g" of internal surface. The macropores are created during polymerization by a solvent from which the polymer precipitates as it is formed. A macroporous polymer is usually, but not necessarily, highly cross-linked. In a good solvent, the polymer phase of a macroporous PS also becomes a microporous, solvent-swollen gel. 

Solvents such as dodecane and amyl alcohol are known to mix with styrene and divinyl benzene in all proportions. However, if polymerization is carried out in the presence of these solvents, the polymer chains precipitate because of their limited solubility. Such a system is now subjected to suspension polymerization. The process of bead formation is complicated due to precipitation, and the polymer chains are highly entangled. Each resin particle has large pores tilled with the solvent Unlike macroporous particles, these are opaque and retain their size and shape even when the diluent is removed. These are called macroreticular resins and wUl absorb any solvent filling their voids. 

Following the completion of the polymerization process, the beaded polymer is recovered from the suspension mixture and freed from the stabilizer, diluents, and traces of monomers and initiators. For laboratory and small-scale preparation, repeated washings with water, methanol, or acetone are appropriate. Complete removal of the monomer diluent, solvents, and initiator, especially from macroporous resin, may require a long equilibration time with warm methanol or acetone. In industry, this is usually accomplished by stream stripping. 

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