Franck D’Agosto

Preparation of Hybrid Latex Particles and Core–Shell Particles Through the Use of Controlled Radical Polymerization Techniques in Aqueous Media

The synthesis of hybrid and core–shell nanoparticles using controlled/ living radical polymerization in aqueous dispersed systems is reviewed. The processes involve emulsion, miniemulsion, and dispersion polymerizations as well as grafting techniques, with the aim of producing submicrometric latex particles with well-defined morphologies that might not be accessible via classical radical polymerization. Those morphologies include organic/inorganic hybrids, nanostructured particles, (nano)capsules, and particles with a hydrophobic core and hydrophilic shell.

Completely Miscible Polyethylene Nanocomposites

A route to fully miscible polyethylene (PE) nanocomposites has been established based on polymer-brush-coated nanoparticles. These nanoparticles can be mixed with PE at any ratio, with homogeneous dispersion, and without aggregation. This allowed a first systematic study of the thermomechanical properties of PE nanocomposites without interference from aggregation effects. We observe that the storage modulus in the semicrystalline state and the softening temperature increase significantly with increasing nanoparticle content, whereas the melt viscosity is unaltered by the presence of nanoparticles. We show that the complete miscibility with the semicrystalline polymer matrix and the improvement of thermomechanical properties in the solid state is caused by the PE-coated nanoparticles being nucleating agents for the crystallization of PE. This provides a general route to fully miscibility nanocomposites with semicrystalline polymers.

Polyethylene end functionalization using thia-Michael addition chemistry

Thiol end functionalized polyethylenes (PE-SH, Mn around 1000 g mol−1, Đ < 1.3) were used as nucleophiles in thia-Michael additions with different acrylic molecules. It was found that under commonly used practical conditions the addition to methacrylates was very difficult, whereas addition to acrylates was very efficient. First, block copolymers based on PE and poly(methyl methacrylate) (PMMA) were targeted by reaction of PE-SH with PMMA obtained by catalytic chain transfer polymerization (CCTP). The reaction however failed and detailed model experiments using butanethiol and a dimer of MMA showed that the solubilization temperature of PE-SH was an impediment to the success of the reaction. The lack of reactivity towards PMMA obtained by CCTP and methacrylate functions was advantageously used to react molecules containing both an acrylate and a methacrylate group in the presence of tributyl phosphine (PBu3) to produce methacrylate-type PE macromonomers. The presence of a hydroxyl function on 3-(acryloyloxy)-2-hydroxypropyl methacrylate induced side trans-esterification reactions catalyzed by PBu3. This was overcome by using the hydroxyl free 2-(acryloyloxy) ethyl methacrylate. With the latter, the desired PE macromonomer exhibited a functionality as high as 85%. Alternatively, 2-isocyanatoethyl methacrylate could also be reacted with PE-SH to produce a highly functionalized methacrylate type PE macromonomer (functionality 89%). Eventually, the efficiency of the thia-Michael addition of PE-SH onto poly(ethylene glycol) acrylate (PEG-acrylate) was used to synthesize the PE-b-PEG block copolymer.

Toward Anisotropic Hybrid Materials: Directional Crystallization of Amphiphilic Polyoxazoline-Based Triblock Terpolymers

We present the design and synthesis of a linear ABC triblock terpolymer for the bottom-up synthesis of anisotropic organic/inorganic hybrid materials: polyethylene-block-poly(2-(4-(tert-butoxycarbonyl)amino)butyl-2-oxazoline)-block-poly(2-iso-propyl-2-oxazoline) (PE-b-PBocAmOx-b-PiPrOx). The synthesis was realized via the covalent linkage of azide-functionalized polyethylene and alkyne functionalized poly(2-alkyl-2-oxazoline) (POx)-based diblock copolymers exploiting copper-catalyzed azide-alkyne cycloaddition (CuAAC) chemistry. After purification of the resulting triblock terpolymer, the middle block was deprotected, resulting in a primary amine in the side chain. In the next step, solution self-assembly into core-shell-corona micelles in aqueous solution was investigated by dynamic light scattering (DLS) and transmission electron microscopy (TEM). Subsequent directional crystallization of the corona-forming block, poly(2-iso-propyl-2-oxazoline), led to the formation of anisotropic superstructures as demonstrated by electron microscopy (SEM and TEM). We present hypotheses concerning the aggregation mechanism as well as first promising results regarding the selective loading of individual domains within such anisotropic nanostructures with metal nanoparticles (Au, Fe3O4).

pH-Switchable Stratification of Colloidal Coatings: Surfaces “On Demand”

Stratified coatings are used to provide properties at a surface, such as hardness or refractive index, which are different from underlying layers. Although time-savings are offered by self-assembly approaches, there have been no methods yet reported to offer stratification on demand. Here, we demonstrate a strategy to create self-assembled stratified coatings, which can be switched to homogeneous structures when required. We use blends of large and small colloidal polymer particle dispersions in water that self-assemble during drying because of an osmotic pressure gradient that leads to a downward velocity of larger particles. Our confocal fluorescent microscopy images reveal a distinct surface layer created by the small particles. When the pH of the initial dispersion is raised, the hydrophilic shells of the small particles swell substantially, and the stratification is switched off. Brownian dynamics simulations explain the suppression of stratification when the small particles are swollen as a result of reduced particle mobility, a drop in the pressure gradient, and less time available before particle jamming. Our strategy paves the way for applications in antireflection films and protective coatings in which the required surface composition can be achieved on demand, simply by adjusting the pH prior to deposition.

Synthesis of Nanocapsules and Polymer/Inorganic Nanoparticles Through Controlled Radical Polymerization At and Near Interfaces in Heterogeneous Media

This review describes recent advances in the synthesis of polymeric nanocapsules and polymer/inorganic hybrid nanoparticles where controlled radical polymerization (CRP) has been used in (mini)emulsion systems to restrict the location of polymerization to an interface. For the synthesis of nanocapsules, CRP polymers stabilize the initial miniemulsion droplet interface and are chain- extended mainly towards the center of the droplets, which contain an inert liquid core. For encapsulation of inorganic particles, CRP polymers adsorbed on their surface are chain-extended to form a polymer shell around the inorganic core. Precise control over the structure and composition of the polymers allows their location to be restricted to these interfaces. Polymerization in the subsequent (mini) emulsion system then commences from these specific locations, courtesy of the reactivatable functions. The developed strategies retain the advantages of tradi- tional emulsion or miniemulsion systems, while greatly expanding their potential to generate novel nanostructured functional materials.

One-Pot RAFT Synthesis of Triphenylphosphine-Functionalized Amphiphilic Core-Shell Polymers and Application as Catalytic Nanoreactors in Aqueous Biphasic Hydroformylation

Controlled radical polymerization has recently been used to develop polymers engineered for applications as catalytic nanoreactors. In this contribution, we present the joint development, in our laboratories, of core-cross-linked micelles (CCM) for application under aqueous biphasic conditions through the micellar approach, using triphenylphosphine (TPP) as polymer-anchored ligand and rhodium as catalytic metal for the hydroformylation of 1-octene as a model α-olefin. The polymers were synthesized by a one-pot convergent approach using RAFT as controlling method in water, making use of the polymerization-induced self-assembly (PISA) principle. The article will also show the polymer properties in terms of size, polydispersity, swelling, metal coordination and exchange, and interpenetration. It will also illustrate our initial catalytic studies with focus on the effect of the polymer architecture (ligand nature, ligand density, core size, nature of cross-linking) and of the stirring rate on the catalytic performance (turnover frequency) and catalyst leaching.

Intercalation and structural aspects of macroRAFT agents into MgAl layered double hydroxides.

Increasing attention has been devoted to the design of layered double hydroxide (LDH)-based hybrid materials. In this work, we demonstrate the intercalation by anion exchange process of poly(acrylic acid) (PAA) and three different hydrophilic random copolymers of acrylic acid (AA) and n-butyl acrylate (BA) with molar masses ranging from 2000 to 4200 g mol−1 synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization, into LDH containing magnesium(II) and aluminium(III) intralayer cations and nitrates as counterions (MgAl-NO3 LDH). At basic pH, the copolymer chains (macroRAFT agents) carry negative charges which allowed the establishment of electrostatic interactions with the LDH interlayer and their intercalation. The resulting hybrid macroRAFT/LDH materials displayed an expanded interlamellar domain compared to pristine MgAl-NO3 LDH from 1.36 nm to 2.33 nm. Depending on the nature of the units involved into the macroRAFT copolymer (only AA or AA and BA), the intercalation led to monolayer or bilayer arrangements within the interlayer space. The macroRAFT intercalation and the molecular structure of the hybrid phases were further characterized by Fourier transform infrared (FTIR) and solid-state 13C, 1H and 27Al nuclear magnetic resonance (NMR) spectroscopies to get a better description of the local structure.

Novel technologies and chemistries for waterborne coatings

Over the past decade, we have developed an integrated approach to the study of novel materials, methods and processes for the production of waterborne coatings. This approach is based on a combination of conventional and free radical chemistries, micro-, mini-, and macroemulsion polymerization, and different reactor and dispersion technologies. In this paper, we will show that an integrated approach is one of the more effective ways of developing synergies for the production of waterborne coating materials. Examples will include approaches to develop high solid content, translucent latexes, self-assembling materials, organic and inorganic hybrid latexes, as well as economic means of generating polymerizable miniemulsions for the implementation of these advances in a commercially feasible manner.

Core-Cross-Linked Micelles and Amphiphilic Nanogels as Unimolecular Nanoreactors for Micellar-Type, Metal-Based Aqueous Biphasic Catalysis

Biphasic homogeneous protocols are attractive for catalyzed transformations in industry, especially when conducted with water as the catalyst phase as exemplified by the large-scale Rhone-Poulenc/Ruhrchemie hydroformylation process, but can only be applied when the substrate is sufficiently soluble in the aqueous phase to sustain sufficiently fast mass transport . Different solutions to reduce mass transport limitations include the use of additives to increase the substrate solubility in water or increase the water/organic interface, anchoring the catalyst onto a lower critical solution temperature (LCST) polymer to implement thermomorphic behavior, and anchoring the catalyst to the hydrophobic part of surfactants or amphiphilic block copolymers that self-assemble in the form of micelles in water. The use of catalytic micelles appears as the most attractive approach but is limited by the potential formation of stable emulsions and by loss of free macromolecules during separation. These limitations are removed by cross-linking the macromolecules into a unimolecular nanoreactor. This chapter covers the emerging area of unimolecular catalytic nanoreactors, focusing on transition metal-based catalytic applications. It will also present the synthesis of new types of catalytic unimolecular nanoreactors developed in our laboratories, conceived to function on the basis of the micellar catalysis principle. These nanoreactors consist of either core-cross-linked micelle (CCM) or amphiphilic functionalized nanogels (NG). The proof of principle of their catalytic performance in the aqueous biphasic hydroformylation of 1-octene will also be presented. The catalyst confinement objective which is highlighted in this chapter is process optimization in terms of the catalyst phase recovery and recycling.