Star Polymers by Photoinduced Copper-Catalyzed Azide–Alkyne Cycloaddition Click Chemistry Hatice Busra Tinmaz, Irem Arslan, Mehmet Atilla Tasdelen Department of Polymer Engineering, Faculty of Engineering, Yalova University, Yalova 77100, Turkey Correspondence to: M. A. Tasdelen (E - mail: tasdelen@yalova.edu.tr) Received 15 December 2014; accepted 21 February 2015; published online 00 Month 2015 DOI: 10.1002/pola.27612 ABSTRACT: Well-defined star polymers consisting of tri-, tetra-, or octa-arms have been prepared via coupling-onto strategy using photoinduced copper(I)-catalyzed 1,3-dipolar cycloaddi- tion click reaction. An azide end-functionalized polystyrene and poly(methyl methacrylate), and an alkyne end-functionalized poly(e-caprolactone) as the integrating arms of the star poly- mers are prepared by the combination of controlled polymer- ization and nucleophilic substitution reactions; whereas, multifunctional cores containing either azide or alkyne func- tionalities were synthesized in quantitatively via etherification and ring-opening reactions. By using photoinduced copper- catalyzed azide–alkyne cycloaddition (CuAAC) click reaction, reactive linear polymers are simply attached onto multifunc- tional cores to form corresponding star polymers via coupling- onto methodology. The chromatographic, spectroscopic, and thermal analyses have clearly demonstrated that successful star formations can be obtained via photoinduced CuAAC click reaction. V C 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 00, 000–000 KEYWORDS: click chemistry; copper-catalyzed azide-alkyne cycloaddition; core-first; metal-organic catalysts/organometallic catalysts; photochemistry; photoredox reactions; self-assembly; star polymers; synthesis INTRODUCTION Star polymer is a typical nonlinear macro- molecule consisting of several linear polymer chains con- nected at one central core. 1 Owing to its multiple functionality and compact spherical structure (smaller hydrodynamic volume and radius of gyration), star polymer has lower intrinsic viscosities and melting points than a lin- ear polymer of similar composition and molecular weight. These unique properties generate several potential applica- tions for star polymers, including drug delivery, cosmetics, coatings, membranes, lithography, viscosity modifiers, cataly- sis, separation media, thin films, and many other advanced materials. Depending on the formation sequence of cores and arms, there are three common methodologies namely, (i) “core-first,” (ii) “arm-first,” and (iii) “coupling-onto” that have been used to synthesize star polymers. 2 In the “core- first” strategy, a multifunctional initiator is employed to simultaneously initiate the polymerization of vinylic mono- mers, and thus forming the arms of the star polymer. With this strategy, controlled/living polymerization techniques have been successfully used to produce well-defined stars by the core-first method. 3 This strategy also offers a more pre- cise control over arm number by tailoring the number of functionalities of the multifunctional initiators. In the second strategy, a reaction of living polymeric chains with either a difunctional monomer (crosslinker) or a multifunctional ter- minating agent has been applied to form a densely cross- linked core from which the arms radiate. This strategy also enables the synthesis of star polymers with a highly cross- linked core containing abundant reactive groups, which may potentially be employed for further encapsulation of the active materials such as drugs, metals, and catalysts. 4 In the third strategy, a star polymer is synthesized by coupling of a preformed polymer chain containing reactive end-groups with a multifunctional core. Owing to the slow reaction rates, low efficiency, and selectivity of the coupling reactions, the variety of star polymers that can be synthesized is limited. But now, this trend has been changed after the discovery of highly efficient “click” chemistry reactions. 5 The “click” chem- istry reactions are very useful and versatile toolbox to con- struct star polymers because of their clean and efficient synthetic capacities and mild reaction conditions. 6 In addi- tion, they are considered orthogonal as the components react together in high yield and in the presence of many other functional groups. To illustrate these advantages, the synthe- sis of miktoarm star polymers bearing four or more different kinds of polymeric arms is often difficult or impossible owing to the complexity of the synthetic methodologies that must be implemented. The use of orthogonal click reactions Additional Supporting Information may be found in the online version of this article. V C 2015 Wiley Periodicals, Inc. WWW.MATERIALSVIEWS.COM JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2015, 00, 000–000 1 JOURNAL OF POLYMER SCIENCE WWW.POLYMERCHEMISTRY.ORG ARTICLE