Polymer Brushes via Surface-Initiated Polymerization catalysts in the final polymer brushes might have undesirable consequences for applications, such as in the biomedical or electronic industry. However, some methods, in particular A(R)GET ATRP, have been developed that allow to reduce the amount of copper to the level of a few ppm. 72 Surface-Initiated Reversible-Addition Fragmentation Chain Transfer (SI-RAFT) PolymerizationIn contrast to ATRP, where the equilibrium between the dormant and active, propagating chains is based on reversible termination, reversible-addition fragmentation chain transfer (RAFT) polymerization is based on reversible chain transfer. [114][115][116] A distinct advantage of RAFT polymerization is its relative simplicity and versatility, since conventional free radical polymerizations can be readily converted into a RAFT process by adding an appropriate RAFT agent, such as a dithioester, dithiocarbamate, or trithiocarbonate compound, while other reaction parameters, such as monomer, initiator, solvent, and temperature, can be kept constant. RAFT polymerization has also been successfully used to prepare polymer brushes via surface-initiated polymerization. SI-RAFT can be performed using two different strategies, which use either surface-immobilized conventional free radical initiators or surface-immobilized RAFT agents (Scheme 2). These two different strategies will be discussed in more detail in the following paragraphs.

The generation of polymer brushes by surface-initiated controlled radical polymerization (SI-CRP) techniques has become a powerful approach to tailor the chemical and physical properties of interfaces and has given rise to great advances in surface and interface engineering. Polymer brushes are defined as thin polymer films in which the individual polymer chains are tethered by one chain end to a solid interface. Significant advances have been made over the past years in the field of polymer brushes. This includes novel developments in SI-CRP, as well as the emergence of novel applications such as catalysis, electronics, nanomaterial synthesis and biosensing. Additionally, polymer brushes prepared via SI-CRP have been utilized to modify the surface of novel substrates such as natural fibers, polymer nanofibers, mesoporous materials, graphene, viruses and protein nanoparticles. The last years have also seen exciting advances in the chemical and physical characterization of polymer brushes, as well as an ever increasing set of computational and simulation tools that allow understanding and predictions of these surface-grafted polymer architectures. The aim of this contribution is to provide a comprehensive review that critically assesses recent advances in the field and highlights the opportunities and challenges for future work.

Post-polymerization modification is based on the direct polymerization or copolymerization of monomers bearing chemoselective handles that are inert towards the polymerization conditions but can be quantitatively converted in a subsequent step into a broad range of other functional groups. The success of this method is based on the excellent conversions achievable under mild conditions, the excellent functional-group tolerance, and the orthogonality of the post-polymerization modification reactions. This Review surveys different classes of reactive polymer precursors bearing chemoselective handles and discusses issues related to the preparation of these reactive polymers by direct polymerization of appropriately functionalized monomers as well as the post-polymerization modification of these precursors into functional polymers.

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