Antoine Bousquet

Thiol-alkyne chemistry for the preparation of micelles with glycopolymer corona: dendritic surfaces versus linear glycopolymer in their ability to bind to lectins.

A poly(tert-butyl acrylate) (P(tBA)) with a glycodendric endfunctionality with eight glucose moieties was synthesised in four steps via a combination of esterification, thiol-alkyne conjugation and hetero-Diels-Alder (HDA) cycloaddition. A linear glycopolymer of similar size and composition was also synthesised in order to compare the protein binding characteristics of the polymer with glycodendritic endfunctionality to the linear glycol blockcopolymer. The two amphiphilic polymers were self-assembled in water into micelles. These particles were then tested for their ability to bind to Concanavalin A (Con A). In a turbidity assay, the polymer glycodendron exhibited a significantly faster clustering rate to the lectin as compared to the linear glycopolymer. In a precipitation assay, it is found that significantly less glucose residue is required for binding per Con A for the polymer with the glycodendritic endfunctionality.

Electrostatic assembly of functional polymer combs onto gold nanoparticle surfaces: combining RAFT, click and LbL to generate new hybrid nanomaterials†

Comb polymers have been synthesized using a “grafting-onto” method via a combination of Reversible Addition–Fragmentation Chain Transfer (RAFT) polymerization and hetero-Diels–Alder (HDA) cycloaddition. A random copolymer comprised of tert-butyl acrylate (tBA) and hydroxyethyl acrylate (HEA) was post-modified via a two step process to introduce diene functionality. Polymers synthesized using benzyl pyridin-2-yldithioformate as a RAFT agent were used as the dienophile in a click reaction with polymer bearing diene pendant groups thus forming comb polymers. Polystyrene (PS), poly(n-butyl acrylate) (PnBA), poly(tert-butyl acrylate) (PtBA) and poly(oligoethyleneglycol methyl ether acrylate) (POEGMEA) were then grafted onto P(tBA-r-HEAdiene) backbones using a reaction time of 24 h. The grafting densities of the comb polymers ranged from 100% to 50%, depending on the chemical structure and the molecular weight of the linear side chain, as well as the initial molar ratio of dienophile to diene groups. Hydrolysis of the poly(tert-butyl acrylate) (PtBA) yielded hydrophilic or amphiphilic polymers with a poly(acrylic acid) (PAA) backbone. Finally a layer-by-layer approach was utilized to build up an initial layer of poly(ethylene amine) followed by a layer of PAA-g-POEGMEA onto gold nanoparticles (GNPs) yielding hybrid organic/inorganic nanoparticles. UV-vis spectroscopy, zeta-potential measurement and X-ray photoelectron spectroscopy (XPS) were used to characterize the hybrid nanoparticles showing that the POEGMA surface layer can shield the charges of the outer layer effectively.

Fabrication and Superhydrophobic Behavior of Fluorinated Microspheres

We describe the preparation of fluorinated microspheres by precipitation polymerization and their use to fabricate superhydrophobic surfaces. For that purpose, two different approaches have been employed. In the first approach, a fluorinated monomer (either 4-fluorostyrene or 2,3,4,5,6-pentafluorostyrene) was added to the initial mixture of monomers constituted by styrene (S) and divinylbenzene (DVB). The second approach is based on the encapsulation of a block copolymer, polystyrene-b-poly(2,3,4,5,6-pentafluorostyrene), during the polymerization of the monomers (S and DVB), thus enabling the formation of particles with perfluorinated chains instead of single functional groups at the interface. Both approaches led to narrow polydisperse particles with fluoro-functional groups at the interface as demonstrated by scanning electron microscopy (SEM), infrared (IR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). Surface array of particles obtained by simple solvent casting presented superhydrophobic behavior with contact angles of water droplets of ca. 160-165°.

Control of the Surface Properties in Polymer Blends

We report on the preparation of amphiphilic diblock copolymers containing a hydrophilic segment, poly(acrylic acid)(PAA), and a polystyrene hydrophobic part. We analysed, by means of contact-angle measurements, how the hydrophilic segments usually bury themselves under the hydrophobic when exposed to air to reduce the surface free energy of the system. In contrast, in contact with water, the hydrophilic blocks have a tendency to segregate to the interface. We first describe the parameters that control the surface reconstruction when the environmental conditions are inversed from dry air to water vapour. Then, annealing time, temperature, composition and size of the diblock copolymers, and size of the matrix that influenced the surface migration process are the main parameters also considered. Finally, the density of the carboxylic functions placed at the surface was determined using the methylene blue method.

Design of polypeptide-functionalized polystyrene microspheres.

In this contribution, the principle of spontaneous surface segregation has been applied for the preparation of polypeptide-functionalized polystyrene microspheres. For that purpose, an amphiphilic diblock copolymer was introduced in the mixture styrene/divinylbenzene and polymerized using AIBN as initiator. During the polymerization, cross-linked particles were obtained in which the diblock copolymer was encapsulated. The amphiphilic diblock copolymers used throughout this study contain a hydrophilic polypeptide segment, either poly(L-lysine) or poly(L-glutamic acid) and a hydrophobic polystyrene block. After 4 h of polymerization, rather monodisperse particles with sizes of approximately 3-4 microm were obtained. Upon annealing in hot water, the hydrophilic polypeptides migrate to the interface, hence, either positively charged or neutral particles were obtained when poly(L-lysine) is revealed at the surface and exposed to acidic or basic pH, respectively. On the opposite, negatively charged particles were achieved in basic pH water by using poly(L-glutamic acid) as additive. The surface chemical composition was modified by changing the environment of the particles. Thus, exposure in toluene provoked a surface rearrangement, and due to its affinity, the polystyrene block reorients toward the interface.

Surface-initiated polymerization of A–A/B–B type conjugated monomers by palladium-catalyzed Stille polycondensation: towards low band gap polymer brushes

A surface-initiated polycondensation which enables access to well-defined core–shell nanoparticles is described. Stille polymerization was initiated from the surface of palladium catalyst-immobilized zinc oxide nanorods. For the first time, a low band gap polymer, poly[(4,4′-bis(2-ethylhexyl)dithieno-[3,2-b:2′,3′-d]silole)-2,6-diyl-alt-(2,1,3-benzothiadiazole)-4,7-diyl] (PSBTBT), was anchored on zinc oxide nanorods to create hybrid materials with tunable photophysical properties.

Environmentally responsive particles: from superhydrophobic particle films to water-dispersible microspheres.

We describe the preparation, by precipitation copolymerization, of multifunctional divinylbenzene-co-pentafluorostyrene microspheres able to produce superhydrophobic surfaces or disperse in aqueous media upon annealing either in air or water, respectively. For that purpose, an amphiphilic block copolymer, polystyrene-b-poly(acrylic acid), was introduced in the initial feed composed of divinylbenzene and 2,3,4,5,6-pentafluorostyrene. As a result, fluorinated particles were obtained in which the diblock copolymer was encapsulated during the polymerization step. Upon annealing in dry air, the particles are completely hydrophobic and form superhydrophobic surfaces. On the contrary, annealing in water induces the reorientation of the PAA groups toward the particle interface, thus the particles can be dispersed in aqueous media. In addition, the presence of carboxylic acid groups at the particle interface permits us to switch the surface charge between negative and neutral depending on the environmental pH.

Crucial Role of the Electron Transport Layer and UV Light on the Open-Circuit Voltage Loss in Inverted Organic Solar Cells

Understanding the degradation mechanisms in organic photovoltaics is crucial in order to develop stable organic semiconductors and robust device architectures. The rapid loss of efficiency, referred to as burn-in, is a major issue to be addressed. This study reports on the influence of the electron transport layer (ETLs) and UV light on the drop of open-circuit voltage (Voc) for P3HT:PC60BM-based devices. The results show that Voc loss is induced by the UV and, more importantly, that the ETL can amplify it, with TiOx yielding a stronger drop than ZnO. Using impedance spectroscopy (IS) and X-ray photoelectron spectroscopy (XPS), different degradation mechanisms were identified according to whether the ETL is TiOx or ZnO. For TiOx-based devices, the formation of an interface dipole was identified, resulting in a loss of the flat-band potential (Vfb) and, thus, of the Voc. For ZnO-based devices, chemical modifications of the metal oxide and active layer at the interface were detected, resulting in a doping of the active layer which impacts the Voc. This study highlights the role of the architecture and, more specifically, of the ETL in the severity of burn-in and degradation pathways.

Nanostructured Interfaces by Surface Segregation of Block Copolymers

Surface modification both in terms of topography and surface functionality appears to be crucial for the development of polymeric materials for particular applications. Variations of the surface topography have been typically accomplished using different strategies based on recent technological advances such as lithography or nanoimprinting among others. Equally, changes on the chemical composition requires surface treatments either using physical approaches or chemical reactions. In general, either parameters functional groups at the surface and topography have been considered separately or the reports described combining both aspects require the use of multistep procedures. In this chapter we revise an alternative to obtain nanostructured and microstructured interfaces having in addition a particular chemical composition. The strategy reported herein takes advantage of the surface thermodynamics to induce the migration of a particular additive towards the interface. Surface segregation is the result of the preferential migration of one blend component to the interface thereby inducing selective enrichment at the near-surface level.As reported here, the use of block copolymers as additives may result in nanostructured domains at the interface. The strategies, alternatives, and methodologies reported to prepare such interfaces are thoroughly described in this chapter.