IntroductionThe azide/alkyne 'click' reaction [1] (also termed the Sharpless 'click' reaction) is a recent re-discovery of a reaction fulfilling many requirements for the affixation of ligands onto polymers by post-modification processes, which include a) often quantitative yields, b) a high tolerance of functional groups, c) an insensitivity of the reaction to solvents, irrespective of their protic/aprotic or polar/ non-polar character, and d) reactions at various types of interfaces, such as solid/liquid, liquid/liquid, or even solid/ solid interfaces. The present review focuses on issues related to the reaction itself as well as on the wide applications in polymer science, material, and surface science.The basic reaction, which is nowadays summed up under the name 'Sharpless-type click reaction', is a variant of the Huisgen 1,3-dipolar cycloaddition reaction [2a,2b] between C-C triple, C-N triple bonds, and alkyl-/aryl-/ sulfonyl azides (see Scheme 1).The relevant outcomes of this reaction are tetrazoles, 1,2,3-triazoles, or 1,2-oxazoles (Scheme 1a-c, respectively). Besides the 1,3-dipolar cycloaddition reaction, classical Diels-Alder-type reactions (Scheme 1d) have been used extensively for the functionalization of polymeric materials and surfaces. [3] These reactions are located within a series of reactions named click reactions, which is defined by a gain of thermodynamic enthalpy of at least 20 kcal Á mol À1 , [1] thus leading to reactions characterized by high yields, simple reaction conditions, fast reaction times, and high selectivity. Among many reactions tested, the 1,3-dipolar cycloaddition process has emerged as the method of choice to effect the requirements of ligating two ReviewThe modification of polymers after the successful achievement of a polymerization process represents an important task in macromolecular science. Cycloaddition reactions, among them the metal catalyzed azide/alkyne 'click' reaction (a variation of the Huisgen 1,3-dipolar cycloaddition reaction between terminal acetylenes and azides) represents an important contribution towards this endeavor. They combine high efficiency (usually above 95%) with a high tolerance of functional groups and solvents, as well as moderate reaction temperatures (25-70 8C). The present review assembles recent literature for applications of this reaction in the field of polymer science (linear polymers, dendrimers, gels) as well as the use of this and related reactions for surface modification on carbon nanotubes, fullerenes, and on solid substrates, and includes the authors own publications in this field. A number of references (>100) are included.

The metal catalyzed azide/alkyne ‘click’ reaction (a variation of the Huisgen 1,3‐dipolar cycloaddition reaction between terminal acetylenes and azides) has vastly increased in broadness and application in the field of polymer science. Thus, this reaction represents one of the few universal, highly efficient functionalization reactions, which combines both high efficiency with an enormously high tolerance of functional groups and solvents under highly moderate reaction temperatures (25–70 °C). The present review assembles an update of this reaction in the field of polymer science (linear polymers, surfaces) with a focus on the synthesis of functionalized polymeric architectures and surfaces.magnified image

The present paper investigates the selective incorporation of preformed nanoparticles (hydrophobic Au-NP (2 nm); hydrophilic Au-NP (12 nm); hydrophobic CdSe-NP (1.9 nm); retrovirus-particles (approximately 30 nm)) into the interface of lipid vesicles and polymersomes via TEM and DLS investigations. Lipid membranes were made from N,N-dimethyl-N,N-dioctadecylammonium bromide (DODAB), di-oleoyl-phosphatidylcholine (DOPC), whereas polymersome-membranes were fabricated from the diblock copolymer poly-(butadiene-block-ethylenoxide). Stabilization of the final structures was achieved via sol/gel processes at the outside of the membranes, thus stabilizing the structure by a silicate shell. Whereas hydrophobic Au-NPs can be successfully embedded into the polymersome- and lipid-vesicle membranes, hydrophilic nanoparticles were found evenly distributed in the inner- and outer compartments of the vesicles and polymersomes. Significant effects such as size reduction, selective enrichment of all nanoparticles within only few polymersomes as well as budding effects of larger entities (i.e., viral particles) are described.

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A new, simple and highly versatile method for the surface modification of luminescent cadmium selenide nanoparticles (CdSe NPs) based on 1,3-dipolar cycloaddition reactions is described. Uniform, trioctylphosphine oxide (TOPO)-covered CdSe NPs were prepared and subjected to two ligand-exchange reactions: first, ligand exchange was accomplished with pyridine, fully removing the TOPO ligand from the CdSe surface. In a second step, either 1-[(3-azidopropyl)octylphosphinoyl]octane or hex-5-ynoic acid 3-(dioctylphosphinoyl)propyl ester were added, attaching an azido or an acetylene moiety to the NP surface. Further thermal or Cu(I)-mediated 1,3-dipolar cycloaddition reactions on the residual azido/acetylene moieties with a variety of acetylenes/azides furnished the modified CdSe NPs with supramolecular receptors (i.e. barbituric acid, thymine, oligoethyleneglycol) on their surface. Photoluminescence measurements reveal a y50% residual quantum yield (relative to TOPO-covered CdSe NPs) after ligand modification, thus presenting an efficient pathway towards luminescent, surface modified CdSe NPs. The presence of the different functional groups was proven by 1 H-NMR, 31 P-NMR spectroscopy and by use of a nanoparticle-bound spiropyran dye and subsequent fluorescence quenching experiments. In order to further exploit the ligands on the CdSe NP surfaces, supramolecular recognition via binding to self-assembled monolayers (SAMs) presenting the matching receptor was investigated, leading to dense layers of CdSe NPs on planar surfaces as verified by AFM measurements. The concept offers a simple method for guiding the binding and recognition of luminescent CdSe NPs and related NPs onto surfaces.