Havingbrieflyexaminedthestructureoforganicpackingsandthevariousroutesintheirmanufacture,themostimportantfeaturesmaybesummarizedasfollows:>Hydrophilicaswellaslipophilicorg... Having briefly examined the structure of organic packings and the various routes
in their manufacture, the most important features may be summarized as follows:
> Hydrophilic as well as lipophilic organic packings are synthesized with a controlled
pore and surface structure depending on the type of monomer/comonomer
and the polymerization reaction. Surface structure can be altered by
controlled consecutive surface reactions.
> In accordance with the bulk composition, polymer packings are stable across
almost the entire pH range, particularly under strong alkaline conditions.
> Chemical stability is affected by oxidizing and reducing solutions.
> Although cross-linking reactions have been optimised in as much as rigid pressure
stable particles can be manufactured, some remaining swelling property is
often noted when changing the solvent composition in HPLC.
> As in the manufacture of silica, porosity, pore size, and surface area of polymer
packings can be adjusted over a wide range, and micro-, meso-, and macro- as well
as non-porous beads are synthesized reproducibly.
3.2.4.2 Hydrophobic Polymer Stationary Phases
The synthesis of cross-linked copolymers of styrene and divinylbenzene has been
studied intensively and is well documented. The starting monomer is styrene, and
divinylbenzene (DVB) is used as cross-linker. The amount of DVB can reach up to
55wt.%. At 55% DVB, the copolymer shows practically no swelling and possesses a
permanent porosity. Figure 3.21 illustrates the network structure of poly(styrenedivinylbenzene)
(St-DVB).
Commercial products differ in bead size and pore size. There are even non-porous
products on the market, designed for the rapid separation of peptides and proteins
by reversed phase HPLC (Maa and Horvath, 1988). St-DVB copolymers are stable in
the pH range 0–14. They find increasing application in the separation of low molecular
weight compounds, peptides, and proteins by means of reversed phase chromatography
(Tanaka et al., 1987, Tweeten and Tweeten, 1986) and as parent materials
for the synthesis of derivatized packings in interaction chromatography of biopoly-mers (Unger et al., 1987, Regnier, 1987). Numerous other organophilic polymer
packings have been synthesized for size exclusion and interactive HPLC after suitable
derivatization. They are reviewed in depth by Mikes (1988).
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