Poly(octadecyl acrylate), ODA(n), with a trimethoxysilyl group at one side of the terminal group was immobilized onto porous silica by using the reactive terminal group. The silica-supported ODA(n) underwent crystalline-to-isotropic phase transition. Interaction between ODA(n) and azobenzenes were evaluated by retention time in the liquid chromatography using the column packed with silica-supported ODA(n). The chromatograph showed complete separation against the geometrical isomers of azobenzenes in methanol-water. The temperature dependence of the separation factor indicated that the selectivity increased with the molecular orientation of ODA(n). Effect of carbonyl-pi interaction due to the acrylate moiety on the selectivity was examined using seven kinds of p-substituted phenylazobenzenes with various Hammett's substituent constants. (C) 1999 Elsevier Science Ltd. All rights reserved.