Divinylbenzene, cross-linking with

Two classes of micron-sized stationary phases have been encountered in this section silica particles and cross-linked polymer resin beads. Both materials are porous, with pore sizes ranging from approximately 50 to 4000 A for silica particles and from 50 to 1,000,000 A for divinylbenzene cross-linked polystyrene resins. In size-exclusion chromatography, also called molecular-exclusion or gel-permeation chromatography, separation is based on the solute s ability to enter into the pores of the column packing. Smaller solutes spend proportionally more time within the pores and, consequently, take longer to elute from the column. 

A typical system is a chlorome thy late d polystyrene resin cross-linked with 2 or 4% p-divinylbenzene and different amounts of chloromethylated sites (0.7—3.7 mequiv. of Cl per g of polymer) . The reaction is shown schematically in Eq. (6.19) and additional information may be found in Sects. 8.3 and 8.8. 

TosoHaas columns are styrene cross-linked with divinylbenzene (DVB). Columns of similar composition are available from Polymer Laboratories (PL Gel), Waters (Ultrastyragel), Shodex, Jordi (JordiGel), and many others. Columns based on derivatized silica are also available, but are less widely used. 

Resin bead polymer composition Either acrylic resins or, more generally, styrene (vinylbenzene, VB) are cross-linked with typically 4 to 20% divinylbenzene (DVB) in a copolymer network or matrix. 

Figure 8. 31P-CP/MAS solid-state spectrum of polymer-bound (polystyrene cross-linked with 2% divinylbenzene) triphenylphosphine (a), 31P-CP/MAS solid-state spectrum of cis-[PtCl2(PPht-C6H -CH—CH2)2] (referenced to external 85% Hs POJ (b), 31P-CP/MAS solid-state spectrum of a copolymer of 65% styrene, 31% divinylbenzene and 4% cis-/PtCl2(PPh2-C6H -CH CH2)z] after soxhlet extraction (c) and 31P-CP/MAS solid-state spectrum of c s-[PtCl(PPhs)2, (N P )] ClOf after soxhlet extraction (d). All spectra referenced to external 85% HsPOk. (Reproduced from Ref. 21. Copyright by American Chemical Society.)...

Starting from the corresponding hydroxymethyl-benzocrown, it has been possible to generate the immobilized system (186) by reacting the above precursor with chloromethylated polystyrene (which is available commercially as Merrifield s resin). Typically, systems of this type contain a polystyrene matrix which has been cross-linked with approximately 1-4% p-divinylbenzene. In one study involving (186), a clean resolution of the alkali metal halides was achieved by HPLC using (186) as the solid phase and methanol as eluent (Blasius etal., 1980). In other studies, the divalent alkaline earths were also separated. 

Among the earliest studies was that of Moffat (105). Poly-2-vinylpyri-dine, cross-linked with 4-8% divinylbenzene, was used as the coordinating support. The amount of cross-linking was found to be critical too little gave a soluble polymer, while too much gave an intractable material which absorbed little metal. Cobalt was used as the catalyst, and the reaction was conducted at 150°-200°C and 2000-3000 psi of 1/1 H2/CO. 

Allen (106) also studied cobalt hydroformylation with a polymer-bound catalyst. The polymer was formed from diphenyl-p-styrylphosphine cross-linked with divinylbenzene. 2-Hexene was the substrate, and reaction conditions were 175°C and 1500-3000 psi of 1/1 H2/CO. The product aldehyde was 55% linear, and the effluent product solution contained 20-50 ppm cobalt. 

With a view to producing catalysts that can easily be removed from reaction products, typical phase-transfer catalysts such as onium salts, crown ethers, and cryptands have been immobilized on polymer supports. The use of such catalysts in liquid-liquid and liquid-solid two-phase systems has been described as triphase catalysis (Regen, 1975, 1977). Cinquini et al. (1976) have compared the activities of catalysts consisting of ligands bound to chloromethylated polystyrene cross-linked with 2 or 4% divinylbenzene and having different densities of catalytic sites ([126], [127], [ 132]—[ 135]) in the... 

Currently available BAS include cholestyramine, colestipol and colesevelam hydrochloride (colestimide). Cholestyramine comprises a long-chain polymer of styrene with divinylbenzene trimethylbenzylammonium groups, whereas colestipol is a long-chain polymer of l-chloro-2,3-epoxypropane with diethylenetriamine. Colesevelam HCl is poly(allylamine hydrochloride) cross-linked with epichlorohydrin and alkylated with 1-bromodecane and 6-bromo-hexyl-trimethylammonium bromide. Bile-acid binding is enhanced and stabilised in the latter compound by long hydrophobic sidechains, increased density of primary amines, and quaternary amine sidechains. For this reason, colesevelam HCl exhibits increased affinity, specificity and capacity to bind bile acids compared with the other BAS. Colesevelam HCl also binds dihydroxy and trihydroxy bile acids with equal affinity, contrasting with cholestyramine and colestipol that preferentially bind dihydroxy bile acids (CDCA and deoxycholic acid). The latter BAS can lead to an imbalance towards trihydroxy bile acids and a more hydrophilic bile-acid pool. 

MTO supported on poly(4-vinylpyridme) 25% cross-linked with divinylbenzene. 

Poly(4-vinylpyridine) resins 6 cross-linked with 9.6 % divinylbenzene and 68-82 % alkylated also have been tested as catalysts for reaction of 1-bromooctane with cyanide ion 81). The catalytic activities depended on the organic solvent in the order benzene > toluene > o-dichlorobenzene. No swelling data were reported, so it is not known if the activities correlate with the swollen volumes of the catalysts. 

HMS-C-SbFi = SbF2 supported on hexagonal mesoporous silica. h MTO supported on poly(4-vinylpyndine) 25% cross-linked with divinylbenzene. 

Figure 1.8 shows an electron micrograph of latex particles made from polystyrene cross-linked with divinylbenzene. Note that these latex particles are not the same as simple polystyrene molecules in a true solution. The particles shown in the figure display a remarkable degree of homogeneity with respect to particle size. Such a sample is said to be monodisperse (in size), in contrast to polydisperse systems, which contain a variety of particle sizes. We have a good... 

Polystyrene and its divinylbenzene cross-linked copolymer have been most widely exploited as the polymer support for anchoring metal complexes. A large variety of ligands containing N, P or S have been anchored on the polystyrene-divinylbenzene matrix either by the bromination-lithiation pathway or by direct interaction of the ligand with C1-, Br- or CN-methylated polystyrene-divinyl-benzene network [14] (Fig. 7). 

Similarly, cobalt(ll)-pyridine (CoPy) complexes bound to copolymers of styrene and acrylic or methacrylic acid, cross-linked with divinylbenzene, catalyze the autoxidation of tetralin dispersed in water at 50°C and 1 bar.45 The rate of oxidation with the colloidal CoPy catalyst was twice as fast as with homogeneous CoPy and nine times as fast as with cobalt(II) acetate in acetic acid. 

Ainberlyst-type catalysts were as active as and more selective than the best homogeneous catalyst, II2SO4. Amberlyst 15 and 3G are macroreticular type polystyrene sulfonic acid resins partially cross-linked with divinylbenzene. The absence of the N—benzyl product when solid acid catalysts were employed suggests the possibility that the reaction could be carried out in a single step. It is also expected to provide all the aforementioned advantages of solid catalysts over liquid catalysts. 

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