Acid and Pseudomonas (P.) cepacia lipase catalyzed ester hydrolysis were evaluated for block copolymer micelles generated from low polydispersity PEG(45)-b-PBOn-b-PCL60 (n = 0, 6, 9). Moving the hydrophilic hydrophobic junction away from the PCL micelle core water interface by inserting a short hydrophobic non-hydrolyzable PBO segment between the PEG and PCL blocks was studied as a strategy for tuning the micelle hydrolytic stability. H-1 NMR was applied in evaluating the micelle and solution compositions and to determine kinetic parameters. Acid and lipase catalyzed micelle hydrolysis proceed by distinctly different routes. Micelles from the triblock copolymers PEG(45)-b-PBOn-b-PCL60 (n = 6, 9) are observed to react substantially slower and persist intact longer in the presence of both strong acids and lipase enzymes than micelles of the parent diblock copolymer (PEG(45)-b-PCL60). (c) 2013 Elsevier Ltd. All rights reserved.