An improved drug delivery system was developed, which enhances the cellular uptake by stabilizing the micelle via core crosslinking resulting in the formation of stable core–shell particles and by decorating the micelles with arginine-glycine-aspartic acid (RGD) containing peptides. In order to generate stable core–shell nanoparticles, block copolymers composed of poly(oligo(ethylene glycol) methyl ether methacrylate)-block-polystyrene-co-poly(3-isopropenyl-α,α-dimethylbenzyl isocyanate) (POEGMA-block-P(STY-co-TMI)) were synthesized viareversible addition fragmentation chain transfer (RAFT) polymerization. Depending on the length of the hydrophobic block, self-assembled aggregates such as micelles, rods and large compound micelles were created in the aqueous solutions. The use of a protected aldehyde containing RAFT agent (CTA) allowed the formation of endfunctional block copolymers, producing micelles bearing aldehyde groups incorporated onto the surface allowing further conjugation with a RGD containing peptide after deprotection. The micelles were stabilized by core crosslinking through the reaction of reactive isocyanate groups with hexamethylenediamine forming stable urea containing core–shell particles. Conjugation with a RGD containing linear peptide, GRGDS, resulted in the formation of micelles bearing peptide groups on the surface. Cytotoxicity tests confirmed the biocompatibility of the synthesized crosslinked micelles revealing efficient cell uptake without causing any signs of cell damage. The conjugation of GRGDS to polymeric micelles and the core crosslinking was shown to significantly enhance the cellular uptake.