Synthesis and association properties of thermoresponsive and permanently cationic charged block copolymers Maria Loreta Patrizi a , Marco Diociaiuti c , Donatella Capitani b , Giancarlo Masci a, * a Department of Chemistry, University of Rome La Sapienza, Piazzale Aldo Moro 5, 00185 Rome, Italy b Institute of Chemical Methodologies, CNR, Via Salaria km 29300, 00016 Monterotondo Stazione, Rome, Italy c Dipartimento di Tecnologie e Salute, Istituto Superiore di Sanita, Viale Regina Elena 299, 00161 Roma, Italy article info Article history: Received 25 September 2008 Received in revised form 13 November 2008 Accepted 17 November 2008 Available online 25 November 2008 Keywords: Atom transfer radical polymerization Micellization Thermosensitive abstract Atom transfer radical polymerization (ATRP) was used to prepare thermosensitive cationic block copoly- mers of (3-acrylamidopropyl)-trimethylammonium chloride (AMPTMA) and N-isopropylacrylamide (NIPAAM) with different block lengths. By using ethyl-2-chloropropionate (ECP) as initiator and CuCl/ CuCl 2 /tris(2-dimethylaminoethyl)amine (Me 6 TREN) catalytic system in DMF:water 50:50 (v/v) mixtures at 20  C the polymerization was controlled. The association properties in NaCl aqueous solution were studied as a function of temperature and polymer concentration by dynamic light scattering, NMR spectroscopy, fluorescence spectroscopy and energy filtered-transmission electron microscopy. The block copolymers formed micellar aggregates above the lower critical solution temperature (LCST) of pNIPAAM. The LCST is strongly influenced by the relative length of the two blocks and is significantly higher than that of pure pNIPAAM. The size of core and shell of the micelles is discussed in terms of block copolymer composition. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction In recent years, polymers that can self-assemble in aqueous solution have received more and more attention due to their ability to form nanostructured associated species like micelles or vesicles with a hydrophobic core and a hydrophilic shell [1–4]. One of the most interesting polymeric architectures that are able to give rise to this phenomenon is double hydrophilic block copolymers. This is a special kind of architecture having both the blocks soluble in water in given conditions. By a proper stimulus such as temperature, pH, or ionic strengths, one of the blocks can become insoluble in water and the block copolymer self-assemble by forming micelles or vesicles with the ‘‘sensitive’’ block in the hydrophobic core. Among the available stimulus responsive polymers, thermally responsive materials are advantageous for biological applications because of the stringent pH requirements in mammalian. One of the most interesting ‘‘sensitive’’ polymer is poly(N-isopropylacrylamide) (pNIPAAM), a thermoresponsive polymer which is water soluble at room temperature and is able to give a coil-to-globule transition above 32  C (the LCST, lower critical solution temperature) [5,6]. NIPAAM copolymers have attracted a lot of attention as the LCST in water is close to body temperature and may therefore be useful in the biomedical field as a stimulus-sensitive material. The synthesis of pNIPAAM block copolymers received a significant stimulus by the development of the so-called ‘‘living’’ radical polymerization (LRP). Several pNIPAAM block copolymers have been prepared by both reversible addition–fragmentation chain transfer (RAFT) [7–18] and atom transfer radical polymerization (ATRP) [19–29]. Nevertheless, to our knowledge the direct synthesis of pNIPAAM block copoly- mers with permanently charged quaternized cationic monomers has not been reported yet. Quaternized cationic homopolymers and copolymers are an important class of materials since they exhibit bactericidal and fungicidal activities [30,31] and can be used to develop self-disinfecting surfaces [32]. For instance, they can be used for a number of applications in hospital surfaces and medical devices, filtration devices, plastic applications, food manufacturing, marine applications. Furthermore, recently it has been demon- strated that diblock copolymer micelles comprising a pH sensitive block core and a quaternized cationic block corona can be used as nanosized templates for the deposition of silica from aqueous solutions [33]. Therefore, block copolymers consisting of a hydrophobic or stimuli sensitive block and quaternized cationic hydrophilic block could have very interesting potential applications. Here we report the first example of direct synthesis by ATRP of double hydrophilic block copolymers of NIPAAM with a quaternized acrylamide based monomer, (3-acrylamidopropyl)-trimethylammonium chloride (AMPTMA). Block copolymers with different compositions were * Corresponding author. Tel.: þ39 06 49913677. E-mail address: giancarlo.masci@uniroma1.it (G. Masci). Contents lists available at ScienceDirect Polymer journal homepage: www.elsevier.com/locate/polymer 0032-3861/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2008.11.023 Polymer 50 (2009) 467–474