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

Homopolymers of 7-oxanorborn-2-ene-5,6-dicarboxylic anhydride (ONDCA) and norborn-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 ring-opening metathesis polymerization (ROMP) using initiators of the type Cl(2)Ru(PR(3))(2)(CHAr') (R = phenyl, cyclohexyl, Ar' = C(6)H(5), p-F-C(6)H(5)). Despite the fact that ONDCA is not initiated stoichiometrically by the initiators employed, the block-copolymers are well-defined in the case where the polymerization is started with NBE. The linear polymers and copolymers were coated onto various vinyl-silanized silica materials and subsequently cross-linked employing azobis(isobutyronitrile) (AIBN). The influence of particle size, pore diameter and volume, the specific surface of the inorganic carrier, the influence of the block sizes, and the amounts of coating on the chemical stability of the resulting materials as well as on the separation efficiency and selectivity have been studied. The high hydrophilicity of any ONDCA-containing polymer or copolymer ensures a strong interaction of the mobile phase with the material even in the case of a low organic solvent content ( < 2%). The high selectivity of the stationary phases is demonstrated by fast baseline separations (6-10 min) of various isomeric anilines and lutidines as well as hydroxyquinolines. The complementary use of apolar, NBE-based coatings and highly polar, pure ONDCA-based coatings allows an in depth discussion of the separation mechanism. Tests designed to detect underivatized, accessible surface silanol groups (Engelhardt test) confirmed the quantitative coating of the surface, which also accounts for the significantly elevated pH stability compared to standard silica materials.