Thermally induced radical hydrosilylation for synthesis of C18 HPLC phases from highly condensed sih terminated silica surfaces

Silicon hydride terminated silica surfaces were prepared at high temperatures by a chlorination-reduction sequence. SiH groups are desired for further surface modification as an alternative to the native silanol groups which are unfavorable for RPLC applications. Only few silanol groups remain in these materials and mostly SiH moieties with the highest degree of cross-linking are obtained. The retention properties of basic analytes on the SiH terminated material confirm that the surfaces is mostly free of silanols and that therefore the remaining SiOH groups are bulk species. A reagentless, radical initiated hydrosilylation reaction is introduced for the functionalization of the hydride terminated surface with 1-octadecene. ¹³C CP/MAS NMR and DRIFT spectroscopy demonstrate the reaction of the carboncarbon double bond and the SiH group as well as the linkage of C18 groups to the silica surface. These novel C18 materials show promising performance in RPLC separation, especially for the separation of organic bases.