We report on the synthesis of a thermosensitive polymer brush-supported 4-N,N-dialkylaminopyridine catalyst and the comparison of its catalytic activity with the corresponding linear polymer-supported version in the hydrolysis of p-nitrophenyl acetate (NPA) as well as the effect of lower critical solution temperature (LCST) transition on catalytic activity. The polymer brushes were synthesized from initiator-functionalized silica particles by surface-initiated atom transfer radical polymerization of methoxytri(ethylene glycol) methacrylate and 2-(N-methyl-N-(4-pyridyl) amino)ethyl methacrylate in the presence of a free initiator. Dynamic light scattering studies showed that the onset temperatures of the LCST transition of polymer brushes in pH 7.52 and 7.82 buffers were 42 and 38 degrees C, respectively. Under the same reaction conditions, the net initial rate of the hydrolysis of NPA catalyzed by hairy particles was 70-80% of that catalyzed by the free copolymer at the temperature below the LCST of polymer brushes. With further increasing the temperature above the LCST, the plot of logarithm of net initial rate versus inverse temperature exhibited a shift for the reactions catalyzed by hairy particles and leveled off or decreased slightly in the case of using the free copolymer as catalyst, presumably because the structures of the aggregates of hairy particles and free copolymer chains were different. (c) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2853-2870, 2009