Synthesis of densely grafted (co)polymer brushes, including poly(tert-butyl acrylate) (PtBA), poly(tertbutyl acrylate)-b-poly(styrene) (PtBA-b-PS), and poly(tertbutyl acrylate)-b-poly(butyl acrylate) (PtBA-b-PBA), from 15.8 nm silica nanoparticles (NPs) via a surface-initiated simplified electrochemically mediated atom transfer radical polymerization (SI-seATRP) under constant potential electrolysis conditions is reported for the first time. The rate of polymerization was enhanced by applying more negative potentials, which resulted in an increase in grafting density, up to 0.93 nm(-2). Furthermore, temporal control over the polymerization was achieved by adjustment of the applied potential. The polymers showed narrow molecular weight distributions (D = 1.20-1.32), and polymer-grafted nanoparticles had excellent size uniformity. Dispersions in suitable solvents were stable without any nanoparticle aggregation. Microstructures observed in thin films of densely block copolymer tethered silica NPs suggested that the structure formation process is strongly influenced by the conformation of tethered chains. Hence, microstructure formation in thin films of block copolymer brush particles in which the first block is in the "stretched brush regime" was determined primarily by surface interactions rather than microphase separation.