Charles-André Fustin

Light-Responsive Block Copolymers

Stimuli-responsive polymers are the subject of intense research because they are able to show responses to various environmental changes. Among those stimuli, light has attracted much attention since it can be localized in time and space and it can also be triggered from outside of the system. In this paper, we review light-responsive block copolymers (LRBCs) that combine characteristic features of block copolymers, e.g., self-assembly behavior, and light-responsive systems. The different photo-responsive moieties that have been incorporated so far in block copolymers as well as the proposed applications are discussed.

A versatile strategy for the synthesis of block copolymers bearing a photocleavable junction

Various block copolymers in which the blocks are held together by a photocleavable junction have been synthesized via a one-pot simultaneous ATRP–CuAAC “click” reaction process, and their easy photocleavage has been demonstrated.

Polymeric Micelles Induced by Interpolymer Complexation

The self-assembly of amphiphilic diblock copolymers in block selective solvents is well documented in the scientific literature. It gives rise to micelles in which the insoluble blocks form a core, which is surrounded by a corona that contains the soluble blocks. Another method to trigger micellization consists in introducing additional non-covalent interactions such as electrostatic interactions or hydrogen bonding in an initially soluble block copolymer. The non-covalent complexes that result from these interactions should be insoluble in order to induce micellization. Such insoluble complexes can be generated by mixing, in a non-selective solvent for all the individual blocks, two block copolymers or a block copolymer and a homopolymer, that contain mutually interacting blocks. This mixing process may, therefore, lead to insoluble non-covalent complexes, which further aggregate into micellar cores stabilized by the uncomplexed blocks. Such a strategy has been successfully implemented in both aqueous and non-aqueous solvents to create interesting stimuli-responsive systems, mainly using ionic interactions and hydrogen bonding. This feature article will summarize these approaches.

Self-Assembly and pH-Responsiveness of ABC Miktoarm Star Terpolymers.

This work deals with the self-assembly in water of ABC miktoarm star terpolymers consisting of hydrophobic poly(-caprolactone), hydrophilic poly(ethylene oxide) (PEO), and pH-sensitive poly(2-vinylpyridine) (P2VP). A variety of experimental techniques were used, including dynamic light scattering, transmission electron microscopy, and zeta potential. Special attention was paid to the pH dependency of the supramolecular self-assemblies. A key observation is the capability of the miktoarm terpolymers to form micelles stable over the whole range of pH, although a transition was observed from neutral to highly positively charged nanoobjects upon decreasing pH.

Synthesis and pH-dependent micellization of diblock copolymer mixtures

This work focused on the preparation and the aqueous solution properties of hybrid polymeric micelles consisting of a hydrophobic poly(epsilon-caprolactone) (PCL) core and a mixed shell of hydrophilic poly(ethylene oxide) (PEO) and pH-sensitive poly(2-vinylpyridine) (P2VP). The hybrid micelles were successfully prepared by the rapid addition of acidic water to a binary solution of PCL(34)-b-PEO(114) and PCL(32)-b-P2VP(52) diblock copolymers in N,N-dimethylformamide. These micelles were pH-responsive as result of the pH-dependent ionization of the P2VP block. The impact of pH on the self-assembly of the binary mixture of diblocks-thus on the composition, shape, size and surface properties of the micelles-was studied by a variety of experimental techniques, i.e., dynamic and static light scattering, transmission electron microscopy, Zeta potential, fluorescence spectroscopy and complement hemolytic 50 test.

Tuning block copolymer micelles by metal–ligand interactions

A terpyridine end-capped poly(styrene)-block-poly(tert-butylacrylate) (PS-b-PtBA-[) copolymer has been synthesized by nitroxide-mediated radical polymerization using a terpyridine-functionalized initiator. Micellization of this copolymer was achieved in ethanol, a selective solvent for the PtBA block. The formed micelles consist of a PS core and a PtBA corona. Terpyridine ligands are located at the extremity of the PtBA chains and are available for complexation with metal ions. The effect of the addition of various metal ions to this system was studied in the dilute regime by dynamic light scattering. Whenever the concentration of the micelles is sufficiently low, addition of metal ions only results in the intramicellar complexation of terpyridine-ended PtBA coronal chains. Since terpyridine can either form mono-complexes or bis-complexes with metal ions, different situations have been observed depending on the metal-to-ligand ratio and on the nature of the metal ions. Finally, the possibility to use these metal–ligand complexes to add an additional poly(ethylene oxide) layer on the initial micelles has been demonstrated. This new approach opens a pathway to tune the size, conformation and functionality of coronal chains in block copolymer micelles.

Functionalized Nanoporous Thin Films From Photocleavable Block Copolymers

A polystyrene-block-poly(ethylene oxide) block copolymer bearing a photocleavable junction between the blocks is used to form nanoporous thin films with carboxylic acid functions homogeneously distributed on the pore walls. The presence of the carboxylic acid groups is evidenced by fluorescence spectroscopy after their reaction with a diazomethane functionalized fluorescent dye. In addition, the initial light-responsive thin film, acting as a photoresist, can be easily patterned to selectively generate porosity in predetermined areas. In that way, fluorescent patterns can be obtained as evidenced by fluorescent microscopy.

Discovering new block terpolymer micellar morphologies

The self-assembly of a new type of triblock terpoly(2-oxazoline) was investigated in water revealing vesicular and aggregated cylindrical micellar structures.

Highly Ordered Conjugated Polymer Nanoarchitectures with Three-Dimensional Structural Control

Conductive polymers are a class of materials with vast potential for tomorrows ultra-large-scale technologies as they combine structural and functional diversity with flexible synthesis and processing approaches. A missing component, with their subtle chemical structure, is reliable building at nanoscale. Here we report on the patterning of polyaniline, a prototypical conjugated polymer, with an unprecedented areal patterning order and density exceeding 0.25 teradot/inch(2). With template-confined growth, through platinum-surface-catalyzed polymerization of aniline, highly ordered arrays of distinct polyaniline nanowires are produced with a typical diameter <or=15 nm and aspect ratio higher than 20. Up-scaling is straightforward. Complex three-dimensional structural control is achieved through a direct pattern transfer via resist- and dose-modulated electron beam lithography. The morphology-modulated nanowires self-assemble in key-lock type architectures induced by the structure asymmetry and nonuniformity of the capillary forces associated with the re-entrant features.

Photo-induced micellization of block copolymers bearing 4,5-dimethoxy-2-nitrobenzyl side groups

The synthesis of photocleavable poly(dimethoxynitrobenzyl acrylate)-block-polystyrene block copolymers is described. The UV irradiation of these block copolymers, dissolved in a good solvent for both blocks, selectively cleaves the dimethoxynitrobenzyl protecting groups, leading to carboxylic acid moieties. Since the resulting hydrophilic poly(acrylic acid) block is insoluble in the solvent used, self-assembly of the diblocks into micelles is observed. This light-induced micellization process is further used to trap dyes into the core of the micelles.