The substrate specificity in solvolysis reactions of p-nitrophenyl alkanoates 2 (n = 2-18) catalyzed by 4-(dialkylamino)pyridine-functionalized polymer 1 was examined in buffered aqueous methanol solution at pH 8.0 and 30 degrees C. The chemical reactivity and substrate specificity in this catalytic system were found to be controlled by changing the buffer system. In 1:1 (v/v) methanol-aqueous phosphate buffer solution, macromolecule 1 exhibits substrate specificity for 2 (n = 14) below 1.0 x 10(-5) unit mol L-1, and the substrate specificity changes from 2 (n = 14) to 2 (n = 12) as the concentration of 1 increases to 2.5 x 10(-5) unit mol L-1 and changes again from 2 (n = 12) to 2 (n = 10) when the concentration of 1 increases further to 7.5 x 10-5 unit mol L-1. However, in 1:1 (v/v) methanol-aqueous Tris buffer solution, macromolecule 1 was found to demonstrate the same substrate specificity for 2 (n = 14) when the concentration of 1 is increased from 5.0 x 10(-6) to 1.0 x 10(-4) unit mol L-1. The control of substrate specificity by the change of the buffer system is believed to be unprecedented for catalysis of ester solvolysis.