Click star polymers

Vora A, Singh K, Webste DC (2009) A new approach to 3-miktoarm star polymers using a combination of reversible addition-fragmentation chain transfer(RAFT) and ting opening polymerization (ROP) via/click chemistiy. Polymta 15(13) 2768-2774... 

This chapter will serve to highlight recent advances in polymer science that have been aided by the use of click chemistry. The copper(l)-catalyzed azide-alkyne cycloaddition (CuAAC) and thiol-ene reactions will be discussed first, after which the utilization of these chemical transformations in the construction and fimction-ahzation of a multitude of different polymeric materials will be outlined. Particular attention will be focused on the preparation of highly complex polymer architectures, such as dendrimers and star polymers, which exempHfy the essential role that chck chemistry has assumed in the polymer science community. 

Scheme 30.12 The convergent one-pot synthesis of a three-arm star polymer using poly(N,N-diethylacrylamide) prepared by RAFT polymerization in combination with thiol-ene click" coupling. Reproduced with permission from Ref [107] 2008, The Royal Society of Chemistry.

The use of click chemistry has also influenced the construction of more sophisticated star polymers, such as those with block copolymer arms. Maty-jaszewski has eloquently demonstrated the preparation of three-arm star block copolymers by again combining ATRP with CuAAC click couphng [109]. In these studies the ATRP of styrene, starting from a trifunctional initiator, yielded the three-arm star homopolymer bearing bromide end groups that subsequently were transformed by substitution with sodium azide. CuAAC reaction with PEO-alkyne... 

Scheme 30.13 Synthesis of well-defined three-miktoarm star polymers using a combination of ATRP and CuAAC click" coupling. Amphiphilic star polymers were prepared that contain one hydrophobic arm and two hydrophilic poly(acrylic acid) arms. Reproduced with permission from Ref. [108] 2006, American Chemical Society.

Scheme 30.16 The convergent synthesis of a seven-arm star polymer containing a j6-cyclodextrin core and poly( --caprolactone) arms using CuAAC click chemistry. Reproduced with permission from Ref. [Ill] 2006, The Royal Society of Chemistry.

Symmetric 3-arm star polymers based on the arm-first technique were synthesized by clicking azide end-functionalized PS, PtBuA, or poly(ethylene glycol) (PEG) with a ttialk5me LA. The coupling efficiendes of PS-N3, PtBuA-N3, and PEG-N3 with the triallqme linking agent were 87%, 85%, and 82%, respectively. 

Past and recent polymerization procedures, their combinations, and the contribution of click chemistry serve as powerful tools for the synthesis of novel well-defined star polymers with different architectures and chemistry. The study of these polymers, the simplest branched stmctures, in bulk or solution, has broadened our knowledge/understanding of the properties and behavior of more complex stmctures. Hopefully the commercialized applications of star polymers will be expanded in the future as the fruits of the intense research on these materials. 

The radical-to-anion transformation was further merged with click chemistry for the synthesis of ABC-type miktoarm star polymers. For this purpose, a trifimctional initiator, namely, propargyl 2-hydroxylmethyl-2-(a-... 

Matyjaszewski and Gao synthesized functional polymers by combining ATRP and the click reactions. They also prepared telechelic polymers, star polymers and brush polymers [282]. Formation of telechelic polymers was illustrated as follows ... 

Figure 12.6 Schematic representation of the modular approach of synthesizing (a) block copolymers, (b) star polymers, and (c) graft copolymers by click chemistry. It should be noted that in spite of greatly enhanced ef ciency of click reactions, as compared to more conventional methods, quantitative conversion is dif cult to achieve in the case of dense grafting. (Adapted from Sumerlin and Vogt, 2010.)...

Problem 12.6 Combination of ATRP and the click coupling method provides a simple and ef cient route to the synthesis of various types of star polymers. Discuss, in this context, a feasible procedure for the ef cient synthesis of polystyrene (PSt) three-arm and four-arm star polymers under mild conditions. 

Gao and Matyjaszewski carried out the rst synthesis of PSt star polymers using a combination of ATRP and click chemistry (Gao and Matyjaszewskki, 2006). PSt linear chains with high azide chain-end functionality were prepared and coupled with tri- and tetra-alkyne-containing coupling agents under mild conditions to produce PSt 3-arm and 4-arm polymers, respectively (Scheme P12.6.1). 

Diels-Alder click reactions have been successfully used for the preparation of well-de ned star polymers. Devise methodologies using this route to prepare 3-arm star polymers with uniform arms, core-As, where A is (a) poly(ethylene glycol), (b) poly(methyl methacrylate), and (c) poly(tert-butyl... 

Keywords Click reaction Crosslinked hydrogels Smart polymers Amphiphilic polysaccharides Supramolecular hydrogels Star polymers Ordered polysaccharides Interpenetrating polymer networks Antibiofilm... 

Other complex architectures, such as azobenzene star polymers (Angiolini et al, 2006) and molecular brushes (Lee et al, 2006a), have also been prepared, although their optical data storage capabilities have not yet been explored. Advances in these new macromolecular architectures are generally based on the combination of CRP and click chemistry reactions as a synthetic tool for achieving more complex smart polymers. 

Johnson JA, Baskin JM, Bertozzi CR, Koberstein JT, Turro NJ. Copper-free click chemistry for the in sim crosslinking of photodegradable star polymers. Chem Comm 2008 44 3064-3066. 

The syntheses of well-defined 7- and 21-arm PNIPAAm star polymers possessing -cyclodextrin (/3-CD) cores were achieved via the combination of ATRP and click reactions. A series of alkynyl terminally functionaUzed PNIPAAm (alkyne-PNIPAAm) linear precursors with varying DP were synthesized via ATRP of NIPAAm using propargyl 2-chloropropionate as the initiator. The subsequent click reactions of alkyne-PNIPAM with azido- 8-CD led to the facile preparation of well-defined 7- and 21-arm star polymers [62]. 

However, in the case of star polymers the above-mentioned strategies are not sufficiently active to achieve a full functionalization of the telechelic polymers. Thus, (Figure 3.6a) the use of the azide-alkine click reaction in combination with LCCP (Binder et al, 2004c Binder... 

Roth, T., Groh, P.W., Palfi, V. et al. (2005) Supramolecular three-arm star polyisobutylenes by sharpless-type click reactions. Polymer Preprints, 46,1166. 

For this reason, the focus of this chapter will be on the recent developments (since 2000) in p-star polymers synthesized by the above living anionic polymerization systems, with emphasis on the control of synthetic factors necessary to achieve well-defined structures of p-star polymers, that is, molecular weight, molecular-weight distribution, arm number, and composition. In the last 20 years, rapid progress in living/controlled radical polymerization systems as well as the application of click makes possible the synthesis of several new p-star polymers. Therefore, representative examples will also be described. The syntheses of p-star polymers before 2000 are beyond the scope of this chapter, although they will be briefly described in Section 4.2, since such subjects have been covered elsewhere by several excellent reviews (Hadjichristidis, 1999 Hadjichristidis et al, 2001). 

Scheme 4.18 Synthesis of 3-arm ABC miktoarm star polymers based on living/controlled radical polymerization and click reaction.

In addition to several examples of ABC stars synthesized by the Uving/controUed polymerization systems mentioned above, three different ABCD p-star polymers were synthesized almost at the same time in 2008 using very similar methodologies (combining living/controlled polymerization systems with click chemistry) (Wang et al., 2008 Altintas et al., 2008), and (Yang et al., 2008). 

Scheme 4.19 Synthesis of 4-arm ABCD miktoarm star polymers by combination of living anionic polymerization, living/controlled radical polymerization, and click reaction.

Deng, G., Ma, D., and Xu, Z. (2007) Synthesis of ABC-type miktoarm star polymers by click chemistry, ATRP and ROP. European Polymer Journal, 43,1179-1187. 

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