RAFT polymerization and self-assembly of thermoresponsive poly(N-decylacrylamide-b-N,N-diethylacrylamide) block copolymers bearing a phenanthrene fluorescent a-end group Telmo J.V. Prazeres a, b , Mariana Beija a, b,1 , Marie-The ´re ` se Charreyre a, * , Jose ´ Paulo S. Farinha b , Jose ´ M.G. Martinho b, ** a Unite´MixteCNRS-bioMe´rieux,E ´ cole Normale Supe´rieure de Lyon, 46 Alle´e d’Italie, 69364 Lyon Cedex 07, France b Centro de Quı ´mica-Fı ´sica Molecular and IN – Institute of Nanoscience and Nanotechnology, Instituto Superior Te ´cnico, Av. Rovisco Pais 1,1049-001 Lisboa, Portugal article info Article history: Received 30 September 2009 Received in revised form 20 November 2009 Accepted 25 November 2009 Available online 3 December 2009 Keywords: RAFT polymerization Thermoresponsive block copolymers Fluorescence abstract Phenanthrene a-end-labeled poly(N-decylacrylamide-b-N,N-diethylacrylamide) (PDcA n -b-PDEA m ) block copolymers consisting in a highly hydrophobic block (n ¼ 11) and a thermoresponsive block with variable length (79  m  468) were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. A new phenanthrene-labeled chain transfer agent (CTA) was synthesized and used to control the RAFT polymerization of a hydrophobic acrylamide derivative, N-decylacrylamide (DcA). This first block was further used as macroCTA to polymerize N,N-diethylacrylamide (DEA) in order to prepare diblock copolymers with the same hydrophobic block of PDcA (number average molecular weight: M n ¼ 2720 g mol 1 , polydispersity index: M w /M n ¼ 1.13) and various PDEA blocks of several lengths (M n ¼ 10,000–60,000 g mol 1 ) with a very high blocking efficiency. The resulting copolymers self-assemble in water forming thermoresponsive micelles. The critical micelle concentration (CMC) was determined using Fo ¨rster resonance energy transfer (FRET) between phenanthrene linked at the end of the PDcA block and anthracene added to the solution at a low concentration (10 5 M), based on the fact that energy transfer only occurs when phenanthrene and anthracene are located in the core of the micelle. The CMC (w2 mM) was obtained at the polymer concentration where the anthracene fluorescence intensity starts to increase. The size of the polymer micelles decreases with temperature increase around the lower critical solution temperature of PDEA in water (LCST w 32  C) owing to the thermoresponsiveness of the PDEA shell. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Labeling of polymers with fluorescent groups is an appropriate and useful tool to study intra and intermolecular polymer chain interactions [1–3], to follow coil-to-globule transition [4–6], self- assembly of block copolymers in selective solvents [7], as well as to characterize the interfaces in polymer blends [8] and the morphology of thin polymer films [9]. They can also be used as probes in fluorescence microscopy and imaging [10] and as light- harvesters in solar cells [11]. Polymers bearing fluorophores distributed randomly along the polymer chain can be obtained either by polymerizing statistically a small quantity of a fluorescent comonomer [12] or by labeling polymer precursors with fluorescent dye derivatives [12,13]. However, these synthetic methodologies do not produce polymers with fluorophores located at a specific position such as one or both chain-ends [3,14], or at the common junction of diblock copolymers [7,15,16]. The first monodisperse well-defined polymers bearing a fluo- rophore at a specific position of the chain were prepared by living anionic polymerization using several strategies: use of a fluorescent labeled initiator [16]; reaction of the functional polymer chain-end with a dye derivative [17]; insertion of a fluorophore at the chain- end by a termination labeling reaction [18] and using a bifunctional fluorescent terminator to label diblock copolymers at the junction point [19]. * Corresponding author. Present address: Laboratoire Joliot-Curie et Laboratoire Inge ´ nierie des Mate ´ riaux Polyme `res, ENS, IFR128, 46 Alle ´ e d’Italie 69364 Lyon Cedex 07, France. Tel.: þ33 4 72 72 89 38; fax: þ33 472 72 87 87. ** Corresponding author. Tel.: þ351 218419250; fax: þ351 218464455. E-mail addresses: mtcharre@ens-lyon.fr (M.-T. Charreyre), jgmartinho@ist.utl.pt (J.M.G. Martinho). 1 Present address: Laboratoire des Inte ´ ractions Mole ´ culaires et Re ´ activite ´ Chi- mique et Photochimique, UMR 5623, Universite ´ Paul Sabatier, 31062 Toulouse Cedex 9, France. Contents lists available at ScienceDirect Polymer journal homepage: www.elsevier.com/locate/polymer 0032-3861/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2009.11.055 Polymer 51 (2010) 355–367