Combination of RAFT Polymerization and CuAAC

Using the rst approach, Sumerhn and coworkers (Gondi et al., 2007) synthesized functional telechelic polymers for which two novel azido-functionalized chain trasfer agents (CTAs), namely, (Xn) and (XIII) (see Fig. 12.18), were prepared and employed to mediate the RAFT polymerization of styrene (St) and Af,Af-dimethylacrylamide (DMA) under a variety of conditions. Poly- 

4-cyano-4-methyl-4-thiobenzoylsulfanyl-butyric acid 3-azidopropyl ester (XIII). (Gondi et al., 2007). 

Problem 12.9 (a) Describe the methods of synthesis of the new azido functionalized CTA, (XII) and 

Thongh the high ef ciency, orthogonahty, and simplicity of CuAAC reactions have prompted rapid and extensive adoption of the method in the eld of macromolecular engineering, the use of copper is undesirable and a cause of concern in the context of biomaterials synthesis. This has generated interest in new metal-free azide-alkyne cycloaddition reactions (discussed below) which do not suffer from toxicity issues. 

Though nonactivated cyclooctynes react somewhat slowly with azides, incorporating electron-withdrawing groups on the ring leads to dramatically enhanced rates that are characteristic of 

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