Norbornene-Functionalized PEO-b-PCL: A Versatile Platform for Mikto- Arm Star, Umbrella-like, and Comb-like Graft Copolymers Duc Anh N’guyen, V eronique Montembault, Sandie Piog e, Sagrario Pascual, Laurent Fontaine Institut des Mol ecules et Mat eriaux du Mans, UMR 6283 CNRS – Le Mans Universit e, Avenue Olivier Messiaen, Le Mans Cedex 9 72085, France Correspondence to: L. Fontaine (E-mail: laurent.fontaine@univ-lemans.fr) Received 16 August 2017; accepted 25 September 2017; published online 00 Month 2017 DOI: 10.1002/pola.28876 ABSTRACT: Well-defined in-chain norbornene-functionalized poly(ethylene oxide)-b-poly(E-caprolactone) copolymers (NB-PEO- b-PCL) were synthesized from a dual clickable containing both hydroxyl- and alkyne-reactive groups, namely heterofunctional norbornene 3-exo-(2-exo-(hydroxymethyl)norborn-5-enyl)methyl hexynoate. A range of NB-PEO-b-PCL copolymers were obtained using a combination of orthogonal organocatalyzed ring-opening polymerization (ROP) and click copper-catalyzed azide–alkyne cycloaddition (CuAAC). Ring-opening metathesis polymerization (ROMP) of NB-PEO-b-PCL macromonomers using ruthenium- based Grubbs’ catalysts provides comb-like and umbrella-like graft copolymers bearing both PEO and PCL grafts on each monomer unit. Mikto-arm star A 2 B 2 copolymers were obtained through a new strategy based on thiol–norbornene photoinitiated click chemistry between 1,3-propanedithiol and NB-PEO-b-PCL. The results demonstrate that in-chain NB-PEO-b-PCL copolymers can be used as a platform to prepare mikto-arm star, umbrella-, and comb-like graft copolymers. V C 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 00, 000–000 KEYWORDS: click chemistry; graft copolymers; mikto-arm; nor- bornene; ROMP; thiol–ene; topological polymers INTRODUCTION Polymers having a strained cycloalkene end- group can be polymerized to generate graft or bottlebrush copolymers through the grafting-through or macromonomer technique using the powerful and widely applicable ring- opening metathesis polymerization (ROMP) process. 1,2 Besides ROMP, the carbon–carbon double bond embedded into such (co)polymers can also be engaged into thiol–ene (C@C hydro- thiolation) reactions. Thiol–ene chemistry, that combines the advantages of a typical click reaction with versatility and ease of implementation, has received considerable interest in the areas of materials and polymer science. 3–12 Indeed, thiol–ene reactions can proceed under a variety of conditions, the most common being the radical-initiated addition and the base- catalyzed (thiol-Michael addition) reaction. Because radical thiol–ene chemistry has many advantages such as high toler- ance to functional groups, water and oxygen, and does not require a metal catalyst, the majority of the reported studies have focused on the radical-mediated variant of this reaction. 10 Initiation of radical thiol–ene reactions is most often achieved by irradiation, with or without added photoinitiator. The norbornene moiety is one of the more reactive “ene” substrate for the thiol–ene reaction, 13,14 thus numerous works have been reported about the thiol–norbornene reac- tion for polymer post-functionalization, cross-linking, and hydrogels preparation. 8–12 However, the thiol–norbornene reaction has never been described for the synthesis of block or star-like polymers, with the exception of the work by Walker et al. who recently demonstrated a simple and efficient synthetic approach to multiblock random and alternating copolymers based on the dithiol addition across highly reactive norbornene end-groups of various polymers. 15 This result illus- trates the high reactivity of the norbornene group in thiol–ene reactions, in contrast to past reports that have highlighted the challenges associated with using thiol–ene chemistry with unstrained ene functionalities for polymer–polymer conjuga- tion. 16 In our group, we have devised a number of efficient strategies based on the combination of organocatalyzed ring- opening polymerization (ROP), 17 reversible deactivation radical polymerization techniques, 18 and click chemistry 19 to prepare well-defined (oxa)norbornene-based macromonomers that can be polymerized through ROMP. 20,21 We speculated that norbornenyl-functionalized polymers would act as reactive sub- strates in thiol–ene processes, providing well-defined copoly- mers with different topologies, depending on the thiol reagent. Indeed, AB diblock copolymers having a reaction site either at Additional Supporting Information may be found in the online version of this article. V C 2017 Wiley Periodicals, Inc. JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2017, 00, 000–000 1 JOURNAL OF POLYMER SCIENCE WWW.POLYMERCHEMISTRY.ORG ARTICLE