The functionalization of nanomaterials with dendritic surface moieties was recently demonstrated to be an effective means of displaying biological ligands and potentially modulating the biological properties of these materials. With the aim of extending this surface functionalization approach to biodegradable polymer assemblies, poly(ethylene oxide)-poly-caprolactone (PEO-PCL) block copolymers with terminal azide or methoxy groups were prepared and were assembled to form micelles or vesicles with varying loadings of surface azides. Dendrons bearing peripheral amines, guanidines, or hydroxyls were prepared and conjugated to the assemblies, and the conjugation yields were measured and compared as a function of azide loading and assembly type ( micelle versus vesicle). A small molecule rhodamine derivative was also conjugated, allowing the effect of sterics to be studied. The effects of the surface functionalization on the aggregation state of the assemblies were studied by light scattering and transmission electron microscopy. Overall, the results revealed interesting differences between the two systems with respect to both the reaction yields and the stabilities. Furthermore, micelles functionalized with dendrons bearing peripheral guanidines were found to exhibit enhanced cell uptake relative to control micelles, demonstrating that this approach can be used to modulate the biological properties of the materials. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 2546-2559, 2011