Polymer brushes are a class of thin coatings, where each of chains is tethered to the underlying substrate via one chain end. Densely grafted polymer brushes feature a stretched chain conformation, which in a unique way enhances their lubrication and non-biofouling properties. Polymer brushes also present a high density of functional groups, whose exposure in solvated brushes is useful for catalysis or in medical applications, including diagnostics. Advances in surface-initiated controlled radical polymerizations (SI-CRP) have facilitated the synthesis of high grafting density polymer brushes with a great control over film thickness / polymer molecular weight and composition. These techniques enable access to plethora of polymer architectures. Due to the fact that SI-CRP strategies allow the use of a wide range of monomers, multiple routes for the post-polymerization modification of polymer brushes are possible. Combination of SI-CRP with post-polymerization modification provides possibilities to systematically study architecture- and composition-property relationships of polymer brushes. This Thesis aims to manipulate the topology and crosslinking dynamics of polymer brushes, whose effect on properties of the coatings will help to understand these relationships. Additionally, functions of polymer brushes can be extended by their modification. As an example, incorporation of nanoparticles is a way to provide catalytic functions. Swelling of the nanoparticle – polymer brush assemblies can expose the catalytically active sites and potentially maximize its activities. Chapter 1 provides an overview of manipulation strategies over the composition and topologies of polymer brushes, routes toward their crosslinking and methods for assembly of nanoparticles within polymer brush matrices. Chapter 2 demonstrates a two-step post-polymerization synthetic approach to generate loop polymer brushes with potentially improved non-biofouling and lubrication properties. In the first step, olefin groups are installed at the polymer chain-ends and then metathesis is used to induce loop closure. Chapter 3 presents a synthetic strategy to install different crosslinks onto polymer brush platforms. It comprises a two step-process: surface-initiated atom transfer polymerization (SI-ATRP) to generate a copolymer platform bearing azide groups, and copper(I)-catalyzed alkyne-azide cycloaddition (CuAAC) using propargyl-modified thiol precursors. Multiple crosslinking and decrosslinking cycles are studied under oxidative and reductive conditions. Chapter 4 explores the catalytic properties of 3-dimensional (3D) assemblies of amorphous molybdenum sulfide in polymer brushes as a template. Poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) brushes are grown from highly-oriented pyrolytic graphite (HOPG) and used to bind anionic tetrathiomolybdate through an anion exchange reaction. In a final oxidation step, the polymer-bound tetrathiomolybdate is converted into the amorphous MoSx catalyst. The performance of polymer brush-catalyst system during hydrogen evolution reaction (HER) is studied.