POLYMER-COATED ALUMINA PARTICLES - CORRELATION OF STRUCTURE AND CHROMATOGRAPHIC PERFORMANCE

A study combining structural characterization by solid-state C-13 NMR and measurement of chromatographic performance is reported for a serie s of polymer-coated Unisphere alumina particles. The alumina particles , coated with cross-linked polybutadiene (PBD) or polybutadiene oxide (PBO) or derivatives thereof, can function as the stationary phase in reversed-phase liquid chromatography (RPLC). Cross-polarization magic- angle spinning C-13 NMR spectroscopy allowed detailed characterization of the polymer-coated samples, including comparison of polymer loadin g levels, measurement of olefinic vs aliphatic carbon, and determinati on of 1,2- and 1,4-olefinic units in the PBD portions of the polymers. In situ chemistry, including hydrogenation and reactions of the cross -linked polymers with C-10 and C18 aliphatic chains, was also monitore d by solid-state NMR. The ability of each of the polymer-coated alumin a samples to separate a standard mixture of five organic compounds was evaluated. Correlations between the NMR results and RPLC performance provide insights into those structural features of polymer coatings wh ich are most important in determining their suitability for use in chr omatographic separations. In particular, hydrophobicity is found to be a key parameter in determining a polymer coating's chromatographic pe rformance.