A poly(2-(2-bromopropionyloxy)ethyl methacrylate) (PBPEM) was used as macroinitiator in the synthesis of molecular brushes with poly(4-vinylpyridine) side chains, (P(BPEM-g-4VP). Atom transfer radical polymerization (ATRP) was employed as the polymerization technique. The polymerizations were carried out in DMF at 30°C using a copper–chloride-based ATRP catalyst, which converted all the dormant polymer chain ends to alkyl chloride groups, thus minimizing branching and crosslinking, which occurred when a copper bromide-based catalyst was employed. Tris(2-pyridylmethyl)amine was selected as the ligand due to the high activity of its Cu I complex in ATRP as well as its strong binding to both Cu I and Cu II , which prevented competitive complexation of the monomer or polymer to the metal center. In order to prevent crosslinking via radical coupling, the monomer conversion was kept low (under 3%) and the alkyl chloride end groups of P4VP side chains were converted to alkoxyamines upon activation followed by a reaction with TEMPO radical. Dynamic light scattering measurements showed the hydrodynamic diameter (D H ) of the brushes was pH-dependent. Aggregation of single P(BPEM-g-4VP) brushes in water was very pronounced at high pH values but was observed even when the amount of added HCl was enough to completely protonate the pyridine units (D H =278nm).