Synthesis and Self-Assembly of Diblock Copolymers Bearing 2-Nitrobenzyl Photocleavable Side Groups Jean-Marc Schumers, Olivier Bertrand, Charles-Andre ´ Fustin, Jean-Franc ¸ois Gohy Bio- and Soft Matter (BSMA), Institute of Condensed Matter and Nanosciences (IMCN), Universite ´ catholique de Louvain, Place L. Pasteur 1, Louvain-la-Neuve, Belgium Correspondence to: C.-A. Fustin or J.-F. Gohy (E-mail: charles-andre.fustin@uclouvain.be or jean-francois.gohy@uclouvain.be) Received 7 September 2011; accepted 20 October 2011; published online 9 November 2011 DOI: 10.1002/pola.25069 ABSTRACT: The light-responsive behavior in solution and in thin films of block copolymers bearing 2-nitrobenzyl photo- cleavable esters as side groups is discussed in this article. The polymers were synthesized by grafting 2-nitrobenzyl moieties onto poly(acrylic acid)-block-polystyrene (PAA-b-PS) precursor polymers, leading to poly(2-nitrobenzyl acrylate- random-acrylic acid)-block-polystyrene (P(NBA-r-AA)-b-PS) block copolymers. The UV irradiation of the block copolymers in a selective solvent for PS led to the formation of micelles that were used to trap hydrophilic molecules inside their core (light-induced encapsulation). In addition, thin films consist- ing of light-responsive P(NBA-r-AA) cylinders surrounded by a PS matrix were achieved by the self-assembly of P(NBA-r-AA)- b-PS copolymers onto silicon substrates. Exposing these films to UV irradiation generates nanostructured materials contain- ing carboxylic acids inside the cylindrical nanodomains. The availability of these chemical functions was demonstrated by reacting them with a functional fluorescent dye. V C 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 50: 599–608, 2012 KEYWORDS: atom transfer radical polymerization (ATRP); micelles; microencapsulation; photocleavable group; self-as- sembly; stimuli-sensitive polymers; thin films INTRODUCTION Nowadays, block copolymers have become powerful tools for the preparation of nanostructured materials. 1–4 That success story stems from their ability to self- assemble into well-organized structures at the nanoscale, whether it happens in the bulk, in thin films, or in solution. The principle underpinning this amazing behavior is a microphase separation process governed by the following: (i) the inherent immiscibility of the majority of polymer blocks and (ii) the exis- tence of a link between the different blocks, which keeps the phase separation process limited into space. As a result, no mac- rophase separation occurs and the formation of a wide range of nanostructures can be achieved. Combining stimuli-responsive features with block copolymers enables to produce ‘‘smart’’ polymeric materials, which are able to show sharp responses to environmental changes such as pH, temperature, light, redox, or chemical changes. 4–8 Among them, light is gaining a lot of inter- est due to some unrivaled features. 9–11 For instance, light can be easily triggered and controlled from outside the system as pho- toprocesses usually start/stop when the light is switched on/off. Moreover, many parameters, such as the intensity and the wave- length of light, can be adjusted during the reaction time. Light-responsiveness is usually imparted to block copoly- mers by the incorporation of photosensitive moieties into their structure, either at the junction between two blocks 12–20 or as side-groups located along one or more of the sequen- ces. 21–34 Besides the well-known azobenzenes, derivatives of 2-nitrobenzyl alcohols have become one of the most famous photosensitive moieties used in polymer science. Initially developed as photolabile protecting groups for carboxylic acid and amine groups in organic and peptide synthesis, 35,36 they were progressively introduced in material science since the early 80s. Typically, they were incorporated in polymers for the production of photoresist materials 37–48 and, more recently, in block copolymers for applications such as light- triggered drug delivery and nanoporous materials. 21,10,20,49 Recently, we reported on the light-triggered micellization of diblock copolymers bearing 4,5-dimethoxy-2-nitrobenzyl side groups. 21 Here, we investigate block copolymers bearing 2-nitrobenzyl photocleavable moieties as side groups, which are composed of a poly(2-nitrobenzyl acrylate-random- acrylic acid) sequence, and of a polystyrene block (P(NBA-r- AA)-b-PS). These photocleavable block copolymers will be discussed not only for light-triggered micellization but also for photo-induced formation of nanoporous thin films. The purpose of this work is thus threefold: to present and dis- cuss (i) a convenient synthesis of these P(NBA-r-AA)-b-PS Author Jean-arc Schumers and Author Olivier Bertrand contributed equally to this work. V C 2011 Wiley Periodicals, Inc. WWW.MATERIALSVIEWS.COM JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 50, 599–608 599 JOURNAL OF POLYMER SCIENCE WWW.POLYMERCHEMISTRY.ORG ARTICLE