A new approach to the preparation of large surface area poly(styrene-co-divinylbenzene) monoliths via knitting of loose chains using external crosslinkers and application of these monolithic columns for separation of small molecules

Poly(styrene-divinylbenzene) monoliths have been hypercrosslinked using a Fe³⁺ catalyzed Friedel–Crafts reaction involving three external crosslinkers (1) 4,4′-bis(chloromethyl)-1,1′-biphenyl, (2) α,α′-dichloro-p-xylene, and (3) formaldehyde dimethyl acetal. The first crosslinker was found to produce monoliths with the best chromatographic performance. The effects of a number of variables affecting the hypercrosslinking reaction were studied in detail. These variables included: (i) the temperature and time used for polymerization of the precursor monoliths, (ii) the amount and loading procedure of the external crosslinker and catalyst, and, (iii) the temperature and reaction time of the Friedel–Crafts alkylation. Polymers with extremely large surface areas reaching up to 900 m²/g were obtained using a precursor monolith polymerized for only 2.5 h, and hypercrosslinked with 4,4’-bis(chloromethyl)-1,1′-biphenyl. The increased performance of monoliths modified using this new procedure is comparable to the performance obtained with monolithic polymers containing chloromethylstyrene. However, the preparation of the poly(styrene-divinylbenzene) precursor is simpler than that of conterparts containing chloromethylstyrene. The hypercrosslinked monoliths in capillary columns were tested in an isocratic reversed phase liquid chromatography separation using a mixture comprised of acetone and six alkylbenzenes. Column efficiencies for retained analytes exceeded 70,000 plates/m.