The formation of homopolymer and block copolymer brushes grafted from flat and nanoparticle surfaces via surface-initiated anionic and cationic polymerization methods is reviewed. Unique properties of these chain addition polymerization methods distinguish them from free-radical and living-radical methods, i.e., primarily the formation of charged reactive propagating centers. This involves the use of methods that preserve the reactivity of the charged species, where the monomer, solvent quality, and lack of terminating species allow for grafting to surfaces and for the formation of homopolymer and block copolymers. While these initiators are analogous to solution and bulk methods and adapted to surfaces, their mechanisms do not necessarily follow their counterparts. Several systems for surface-initiated polymerization (SIP) will be reviewed including early attempts at "grafting onto" and "grafting from" particles. For initiation, alkylsilane or alkylthiol anionic initiators are grafted onto planar and particle surfaces by self-assembled monolayer (SAM) techniques. For the cationic (carbocationic) polymerization methods, methods of tethering Lewis acids to surfaces have been reported. The grafted polymer chains can be investigated in situ using a number of surface-sensitive spectroscopic and microscopic techniques. They can also be analyzed ex situ when the polymer chains are removed from the substrate surface. Activation of the grafted initiator, control of polymerization conditions, and removal of excess activators are emphasized. Interesting differences in particle properties, morphology, thickness, grafting density, and polymerization conditions contrast anionic and cationic charged species from other SIP mechanisms. The problems and potential of these techniques will also be discussed. The formation of block copolymer sequences highlights a unique utility of living anionic and cationic polymerization techniques on surfaces.
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