ROMP-based, highly hydrophilic poly(7-oxanorborn-2-ene-5,6-dicarboxylic acid)-coated silica for analytical and preparative scale high-performance ionchromatography

Homopolymers of 7-oxanorborn-2-ene-5,6-dicarboxylic anhydride (ONDCA) and n orborn-2-ene (NBE), respectively, as well as copolymers of ONDCA A and NBE with well-defined block sizes and molecular weights have been prepared by r ing-opening metathesis polymerization (ROMP) using initiators of the type C l2Ru(PR3)(2)(CHAr') (R = phenyl, cyclohexyl, Ar' = C6H5, p-F-C6H5). Despite the fact that ONDCA is not initiated stoichiometrically by the initiators employed, the block-copolymers are well-defined in the case where the polym erization is started with NBE. The linear polymers and copolymers were coat ed onto various vinyl-silanized silica materials and subsequently cross-lin ked employing azobis(isobutyronitrile) (AIBN). The influence of particle si ze, pore diameter and volume, the specific surface of the inorganic carrier , the influence of the block sizes, and the amounts of coating on the chemi cal stability of the resulting materials as well as on the separation effic iency and selectivity have been studied. The high hydrophilicity of any OND CA-containing polymer or copolymer ensures a strong interaction of the mobi le phase with the material even in the case of a low organic solvent conten t ( < 2%). The high selectivity of the stationary phases is demonstrated by fast baseline separations (6-10 min) of various isomeric anilines and luti dines as well as hydroxyquinolines. The complementary use of apolar, NBE-ba sed coatings and highly polar, pure ONDCA-based coatings allows an in depth discussion of the separation mechanism. Tests designed to detect underivat ized, accessible surface silanol groups (Engelhardt test) confirmed the qua ntitative coating of the surface, which also accounts for the significantly elevated pH stability compared to standard silica materials.