1,4-divinylbenzene polymerization

Recently high purity styrene divinylbenzene polymeric gels have become available for use in lipophilic SPE extraction these types of materials formerly contained monomer materials which could interfere in analyses. These types of gels are much more lipophilic than surface-modified silica gels and also have a higher capacity for sample loading. Their applications are similar to those of the lipophilic silica gels. 

Selected data published by Patsias and Papadopoulou-Mourkidou [114] illustrate sorption s dependence on sample volume (Figure 2.36). Their research pursues development of an automated online SPE-HPLC methodology for analysis of substituted anilines and phenols. Recovery (%) was measured for numerous compounds on various polymeric sorbents, but the only data presented here are those in which a styrene-divinylbenzene polymeric sorbent was used for analysis of aniline, phenol, 4-nitroaniline, and 4-nitrophenol. Aqueous sample volumes of 5, 10, 25, 50, 75, 100, 125, and 150 mL were acidified to pH 3 before SPE. 

LC/MS/MS is an important technique for the analysis of free metabolites and covalent adducts of sulfur mustard in urine and blood. In the case of TDG and TDGO, LC/MS has not yet been able to achieve the LODs obtainable with GC/MS after derivatization. LC/MS/MS has, however, been used successfully to analyze the metabolites (20, 21) derived from an initial reaction of sulfur mustard with glutathione (see Chapter 16). The two metabolites (20), derived from the 3-lyase pathway, can be isolated from urine by SPE on a hydroxylated polystyrene-divinylbenzene polymeric cartridge. Using a sensitive triple sector quadrupole LC/MS/MS system, detection limits of O.lng/ml have been achieved using positive ESI and MRM (56). This provides a useful alternative to GC/MS/MS, which requires reduction of the sulfoxide functions with titanium trichloride. An LC/MS/MS method (detection limit lng/ml) has been developed for the analysis of the hisf N - ace ly I cysteine) metabolite (21) in urine (57). Concentration from acidified urine was achieved on... 

A typical mobile-phase composition is an acetonitrile-water gradient with a fixed concentration of trifluoroacetic acid (TFA), formic, or acetic acid (typically 0.05-0.5%). TFA acts as an ion-pairing agent and masks secondary interactions with the silica-based stationary phase. TFA may significantly suppress the ESI response in positive-ion mode. To avoid this, either formic acid is preferred or a mixture of 0.02% TFA and 0.5% acetic acid can be used. Some silica-based RPLC materials can be used with a lower TFA concentration (PepMap ). Alternatively, poly(styrene-divinylbenzene) polymeric materials (PS-DVB) can be applied. With a monolithic PS-DVB column, only a small decrease in separation efficiency on the monolithic column was observed when the TFA concentration was reduced from 0.2%to0.05%[51]. 

Change solid sorbent to one that has a greater affinity for the compound from the sample matrix (i.e., water, urine, etc.). Try the same mechanism of sorption but with a stronger interaction. For example, a compound is too polar for the C-18 bonded phase. Try a styrene-divinylbenzene polymeric sorbent or activated-carbon sorbent. 

In addition to true ion exchange, other interactions can take place between the sample solutes and the resin. Adsorption is one of the commonest of these interactions. For example, the benzoate anion appears to be adsorbed somewhat by the poly-styrene-divinylbenzene polymeric matrix of organic ion exchangers. This may be due to an attraction of the k electrons of the aromatic polymer for the benzoate. Benzoic acid, which exists mostly in the molecular form, is absorbed to a much greater degree than benzoate salts. 

Fmoc-aminomethyl-3,5-dimethoxyphen-oxy)valeric acid PEG, polyethylene glycol PEG-PS, polyethylene glycol-cross-linked polystyrene graft copolymer PS, copoly-(styrene-1% divinylbenzene) polymeric support , resin SPPS, solid-phase peptide synthesis tBu, tert.-butyl TEA, trifluoro-acetic acid TFE, trifluoroethanol THF, te-trahydrofuran TLC, thin-layer chromatography. Amino acid symbols denote the L-con-figuration. All solvent ratios and percentages are v/v unless stated otherwise. 

The organic and aqueous phases are prepared in separate tanks before transferring to the reaction ketde. In the manufacture of a styrenic copolymer, predeterrnined amounts of styrene (1) and divinylbenzene (2) are mixed together in the organic phase tank. Styrene is the principal constituent, and is usually about 90—95 wt % of the formulation. The other 5—10% is DVB. It is required to link chains of linear polystyrene together as polymerization proceeds. DVB is referred to as a cross-linker. Without it, functionalized polystyrene would be much too soluble to perform as an ion-exchange resin. Ethylene—methacrylate [97-90-5] and to a lesser degree trivinylbenzene [1322-23-2] are occasionally used as substitutes for DVB. 

The point at which two polymeric chains are joined together by a cross-linker such as divinylbenzene, or sites where tertiary hydrogens are located in the stmcture, are other locations for oxidative attack. In both cation- and anion-exchange resins, oxidative attack results in the removal of cross-linking. 

Divinylbenzene. This is a specialty monomer used primarily to make cross-linked polystyrene resins. Pure divinylbenzene (DVB) monomer is highly reactive polymericaHy and is impractical to produce and store. Commercial DVB monomer (76—79) is generally manufactured and suppHed as mixtures of m- and -divinylbenzenes and ethylvinylbenzenes. DVB products are designated by commercial grades in accordance with the divinylbenzene content. Physical properties of DVB-22 and DVB-55 are shown in Table 10. Typical analyses of DVB-22 and DVB-55 are shown in Table 11. Divinylbenzene [1321 -74-0] is readily polymerized to give britde insoluble polymers even at ambient temperatures. The product is heavily inhibited with TBC and sulfur to minimize polymerization and oxidation. 

Divinylbenzene copolymers with styrene are produced extensively as supports for the active sites of ion-exchange resins and in biochemical synthesis. About 1—10 wt % divinylbenzene is used, depending on the required rigidity of the cross-linked gel, and the polymerization is carried out as a suspension of the monomer-phase droplets in water, usually as a batch process. Several studies have been reported on the reaction kinetics (200,201). 

Third Monomers. In order to achieve certain property improvements, nitrile mbber producers add a third monomer to the emulsion polymerization process. When methacrylic acid is added to the polymer stmcture, a carboxylated nitrile mbber with greatly enhanced abrasion properties is achieved (9). Carboxylated nitrile mbber carries the ASTM designation of XNBR. Cross-linking monomers, eg, divinylbenzene or ethylene glycol dimethacrylate, produce precross-linked mbbers with low nerve and die swell. To avoid extraction losses of antioxidant as a result of contact with fluids duriag service, grades of NBR are available that have utilized a special third monomer that contains an antioxidant moiety (10). FiaaHy, terpolymers prepared from 1,3-butadiene, acrylonitrile, and isoprene are also commercially available. 

Beaded polymeric support, whether polystyrene-divinylbenzene, polymethacrylate, or polyvinyl alcohol, is conventionally produced by different variations of a two-phase suspension polymerization process, in which liquid microdroplets are converted to the corresponding solid microbeads (1). 

Suspension polymerization of water-insoluble monomers (e.g., styrene and divinylbenzene) involves the formation of an oil droplet suspension of the monomer in water with direct conversions of individual monomer droplets into the corresponding polymer beads. Preparation of beaded polymers from water-soluble monomers (e.g., acrylamide) is similar, except that an aqueous solution of monomers is dispersed in oil to form a water-in-oil (w/o) droplet suspension. Subsequent polymerization of the monomer droplets produces the corresponding swollen hydrophilic polyacrylamide beads. These processes are often referred to as inverse suspension polymerization. 

The pore size, the pore-size distribution, and the surface area of organic polymeric supports can be controlled easily during production by precipitation processes that take place during the conversion of liquid microdroplets to solid microbeads. For example, polystyrene beads produced without cross-linked agents or diluent are nonporous or contain very small pores. However, by using bigb divinylbenzene (DVB) concentrations and monomer diluents, polymer beads with wide porosities and pore sizes can be produced, depending on the proportion of DVB and monomer diluent. Control of porosity by means of monomer diluent has been extensively studied for polystyrene (3-6) and polymethacrylate (7-10). 

Synthetic organic polymers, which are used as polymeric supports for chromatography, as catalysts, as solid-phase supports for peptide and oligonucleotide synthesis, and for diagnosis, are based mainly on polystyrene, polystyrene-divinylbenzene, polyacrylamide, polymethacrylates, and polyvinyl alcohols. A conventional suspension of polymerization is usually used to produce these organic polymeric supports, especially in large-scale industrial production. 

Styrene-based polymer supports are produced by o/w suspension polymerization of styrene and divinylbenzene. Suspension polymerization is usually carried out by using a monomer-soluble initiator such as benzoperoxide (BPO) or 2,2-azo-bis-isobutylnitrile (AIBN) at a temperature of 55-85°C (19). A relatively high initiator concentration of 1-5% (w/w) based on the monomer is used. The time required for complete monomer conversion must be determined by preliminary experiments and is usually between 5 and 20 h, depending on the initiator concentration, the temperature, and the exact composition of the monomer mixture (11-18). 

Producing a polystyrene (PS)-DVB copolymer of increasing porosity has been accomplished by dissolving 50-80% styrene, 10-50% divinylbenzene, and 30-70% of an inert organic liquid. Toluene is a solvent for the monomer but is a nonsolvent for the polymerized polymer. The monomer solution is then incorporated into water to form a dispersion of oil droplets followed by the polymerization of the suspended oil droplets from the aqueous medium into the polymer (21). 

A macroporous polystyrene-divinylbenzene copolymer is produced by a suspension polymerization of a mixture of monomers in the presence of water as a precipitant. This is substantially immiscible with the monomer mixture but is solubilized with a monomer mixture by micelle-forming mechanisms in the presence of the surfactant sodium bis(2-ethylhexylsulfosuccinate) (22). The porosity of percentage void volume of macroporous resin particles is related to percentage weight of the composite (50% precipitant, 50% solvent) in the monomer mixture. 

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). 

New templated polymer support materials have been developed for use as re versed-phase packing materials. Pore size and particle size have not usually been precisely controlled by conventional suspension polymerization. A templated polymerization is used to obtain controllable pore size and particle-size distribution. In this technique, hydrophilic monomers and divinylbenzene are formulated and filled into pores in templated silica material, at room temperature. After polymerization, the templated silica material is removed by base hydrolysis. The surface of the polymer may be modified in various ways to obtain the desired functionality. The particles are useful in chromatography, adsorption, and ion exchange and as polymeric supports of catalysts (39,40). 

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. 

A novel cross-linked polystyrene-divinylbenzene copolymer has been produced from suspension polymerization with toluene as a diluent, having an average particle size of 2 to 50 /rm, with an exclusive molecular weight for the polystyrene standard from about 500 to 20,000 in gel-permeation chromatography. A process for preparing the PS-DVB copolymer by suspension polymerization in the presence of at least one free-radical polymerization initiator, such as 2,2 -azo-bis (2,4-dimethylvaleronitrile) with a half-life of about 2 to 60 min at 70°C, has been disclosed (78). 

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