The polymer micelle poly[(N-(n-dodecyl)-4-vinylpyridinium-co-N-ethyl-4-vinylpyridinium) bromide], PDE(30), promotes selectivity in the hydrolysis of p-nitrophenyl eaters, 1. The hydrolysis rate of 1 (n = 8) is faster than the hydrolysis of 1 (n = 6, 10, 12, and 14) in 0.0125 Pd berate buffer at pH 8.9 and 30 degrees C. Interesting biphasic behavior is observed with increasing concentration of ester, and this is attributed to a change in the organization of the PDE(30)/ester coaggregates. The reported results are believed to be due to the response of a multicomponent system to the formation of differently organized phases with different levels of reactivity in the reaction mixture.