Poly styrene-co-divinylbenzene -Based Polymers

Styrene/divinylbenzene copolymers are the most widely used substrate materials. Because they are stable in the pH range between 0 and 14, eluents with extreme pH values may be used. This allows the conversion of compounds such as carbohydrates, which are not ionic at a neutral pH, into the anionic form, making them available for ion chromatographic analysis (see also Section 3.10). 

In general, a distinction is made between microporous and macroreticular resins. The former are by far more important for anion-exchange chromatography. 

Microporous (gel-type) substrates are prepared by bead polymerization. In this process, the two monomeric compounds, styrene and divinylbenzene, are suspended as small droplets in water by rapid, even stirring. The polymerization is initiated by appropriate catalysts and leads to uniform particles, the 

With the exception of nanobead-agglomerated anion exchangers (see Section 3.4.1.4), where totally porous nanobeads act as ion-exchange material, organic polymers are functionalized directly at their surface. Surface-functionalized, the so-called pellicular substrates, show a much higher chromatographic efficiency than fully functionalized resins. 

The organic polymers mentioned above are functionalized in a two-step process  

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Overview of Surface-Aminated Poly(styrene-co-divinylbenzene)-Based Polymers... 

Poly(styrene-co-divinylbenzene)-based polymers are widely used as substrate materials for the manufecture of cation exchangers. The principal properties of... 

A common characteristic of all poly(styrene-co-divinylbenzene)-based ion-exclusion phases is the high retention of aromatic carboxylic acids. This is due to 3t-3t interactions between the aromatic ring systems of the polymer and the solute. The separation of aromatic carboxyhc adds, therefore, is more elegantly accomplished by reversed-phase chromatography. 

Recent chromatographic data indicate that the interactions between the hydrophobic surface of a molded poly(styrene-co-divinylbenzene) monolith and solutes such as alkylbenzenes do not differ from those observed with beads under similar chromatographic conditions [67]. The average retention increase, which reflects the contribution of one methylene group to the overall retention of a particular solute, has a value of 1.42. This value is close to that published in the literature for typical polystyrene-based beads [115]. However, the efficiency of the monolithic polymer column is only about 13,000 plates/m for the isocratic separation of three alkylbenzenes. This value is much lower than the efficiencies of typical columns packed with small beads. 

A mechanistic study by Haynes et al. demonstrated that the same basic reaction cycle operates for rhodium-catalysed methanol carbonylation in both homogeneous and supported systems [59]. The catalytically active complex [Rh(CO)2l2] was supported on an ion exchange resin based on poly(4-vinylpyridine-co-styrene-co-divinylbenzene) in which the pendant pyridyl groups had been quaternised by reaction with Mel. Heterogenisation of the Rh(I) complex was achieved by reaction of the quaternised polymer with the dimer, [Rh(CO)2l]2 (Scheme 11). Infrared spectroscopy revealed i (CO) bands for the supported [Rh(CO)2l2] anions at frequencies very similar to those observed in solution spectra. The structure of the supported complex was confirmed by EXAFS measurements, which revealed a square planar geometry comparable to that found in solution and the solid state. The first X-ray crystal structures of salts of [Rh(CO)2l2]" were also reported in this study. 

The most widely used polymer monoliths are poly(styrene-co-divinylben-zene)-based monoliths and moderately polar monoliths based on methacrylic acid esters. While the first ones are strongly hydrophobic materials prepared by polymerization of styrene and its derivatives with divinylbenzene as the cross-linking agent [323,324], methacrylate-based monoliths are synthesized by polymerization of butyl methacrylate or other methacrylic acid esters with ethylene dimethacrylate as the cross-linking agent [325,326]. These types of monolithic media in capillary format are the main focus of a very detailed review by Urban and Jandera [327]. 

The structure and reactivity of anionic complexes [M(CO)2l2] (M = Rh, Ir) supported on ion exchange resins based on quaternized poly(4-vinylpyridine-co-styrene-co-divinylbenzene) have been investigated using a variety of techniques. The reactivity toward Mel of [M(CO)2l2l supported on thin polymer films was probed directly in situ by IR spectroscopy. For M = Ir oxidative addition gave a stable Me complex, [Ir(CO)2l3Me] , as observed in solution chemistry. The kinetic measurements represent a rare example of quantitative rate data for fundamental reaction steps of a heterogenized transition metal catalyst. ... 

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