Experimental - Introduction Current technology in the field...

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IntroductionCurrent technology in the field of molecular biology and materials science has driven the need for well-defined microstructures for surfaces and materials. There are several challenges to control the synthesis of these materials. Sugars, DNA, and proteins have had millions of years to develop into their current superstructures whereas manmade materials have developed over the last hundred years. Researchers in material and polymer sciences have been searching for well-defined ligation strategies to work with a variety of different functional groups. Dr. Sharpless in his 2001 review of click reactions, defined click chemistry as a set of powerful, highly reliable, and selective reactions for the rapid synthesis of useful new compounds and combinatorial libraries.1A multitude of compounds have been synthesized viaa simple click reaction of a terminal alkyne to an azide.2Click reactions are driven by a high thermodynamic driving force (>20 kcal mol−1), which is typically associated with the formation of carbon–heteroatom bonds.3As shown in Figure 1, a terminal alkyne is reacted with an azide to form a triazole. The reaction yields high yields at a fast rate compared to a non-catalyzed reaction. Figure 1.Example click reaction.The value of click chemistry for materials synthesis is apparent in polymer chemistry. Several recent reviews have described the use of Cu-catalyzed azide–alkyne cycloaddition (CuAAC) for the synthesis of dendritic, branched, linear and cyclic co-polymers.4Biocompatible polymers synthesized viaAtom Transfer Radical Polymerization (ATRP) have been clicked to viruses.5The combination of click chemistry with Controlled Radical Polymerization (CRP) has contributed to rapid development in the available range of polymer architectures and functional materials. CRP allows for the preparation of polymers with predetermined molecular weight, narrow molecular weight distribution, chain end functionality, and complex architecture and composition.6The most common CRP methods are Atom Transfer Radical Polymerization (ATRP), Nitroxide-Mediated Polymerization (NMP), and Reversible Addition–Fragmentation Transfer
(RAFT). The key to success lies in masking the radical in the form of a dormant species. A dormant species cannot terminate but can be intermittently activated to form a radical that, after addition of a few monomer units, returns into its dormant state. An equilibrium between dormant and growing species is established and the equilibrium is very much shifted toward the dormant state (See Figure 2). Due to the shift in equilibrium, all chains grow steadily at approximately the same rate and therefore a predictable molecular weight (MW) and a narrow polydispersity index (PDI) can be achieved.

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