Jérôme Vinas

An Emulsifier‐Free RAFT‐Mediated Process for the Efficient Synthesis of Cerium Oxide/Polymer Hybrid Latexes

Hybrid latexes based on cerium oxide nanoparticles are synthesized via an emulsifier-free process of emulsion polymerization employing amphiphatic macro-RAFT agents. Poly(butyl acrylate-co-acrylic acid) random oligomers of various compositions and chain lengths are first obtained by RAFT copolymerization in the presence of a trithiocarbonate as controlling agent. In a second step, the seeded emulsion copolymerization of styrene and methyl acrylate is carried out in the presence of nanoceria with macro-RAFT agents adsorbed at their surface, resulting in a high incorporation efficiency of cerium oxide nanoparticles in the final hybrid latexes, as evidenced by cryo-transmission electron microscopy.

Sulfonated macro-RAFT agents for the surfactant-free synthesis of cerium oxide-based hybrid latexes

Three types of amphiphatic macro-RAFT agents were employed as compatibilizers to promote the polymerization reaction at the surface of nanoceria for the synthesis of CeO2-based hybrid latexes. Macro-RAFT copolymers and terpolymers were first synthesized employing various combinations of butyl acrylate as a hydrophobic monomer and acrylic acid (AA) and/or 2-acrylamido-2-methylpropane sulfonic acid (AMPS) as hydrophilic monomers. After characterizing the adsorption of these macro-RAFT agents at the cerium oxide surface by UV-visible spectrometry, emulsion copolymerization reactions of styrene and methyl acrylate were then carried out in the presence of the surface-modified nanoceria. Dynamic Light Scattering and cryo-Transmission Electron Microscopy were employed to confirm the hybrid structure of the final CeO2/polymer latexes, and proved that the presence of acrylic acid units in amphiphatic macro-RAFT agents enabled an efficient formation of hybrid structures, while the presence of AMPS units, when combined with AA units, resulted in a better distribution of cerium oxide nanoclusters between latex particles.

A CeO2/PVDC hybrid latex mediated by a phosphonated macro-RAFT agent

A poly(vinylidene chloride-co-methyl acrylate) hybrid latex comprising CeO2 nanoparticles was successfully prepared by emulsion polymerization employing a water-soluble phosphonated macro-RAFT agent. A poly(vinylbenzylphosphonic diacid-co-styrene) statistical copolymer was first synthesized, using dibenzyl trithiocarbonate as a controlling agent, and adsorbed on ceria nanoparticles. UV-visible and 31P NMR spectroscopy proved to be efficient and complementary techniques to assess the extent of interactions between the copolymer and ceria nanoparticles, leading to a better understanding of the adsorption of phosphonated copolymer chains on inorganic particles. Then, these functionalized-CeO2 nanoparticles were used to mediate the emulsion copolymerization of vinylidene chloride and methyl acrylate in the presence of a very low amount of emulsifier. Cryo-transmission electron microscopy (cryo-TEM) confirmed the hybrid structure of the latex and the absence of either free ceria nanoparticles or free PVDC latex particles.

Selective and Quantitative Oxidation of Xanthate End‐Groups of RAFT Poly(n‐butyl acrylate) Latexes by Ozonolysis

Although various successful strategies have been reported in the past for the postpolymerization modification of the reversible addition-fragmentation chain transfer (RAFT) terminal group in homogeneous media, no solution is proposed for the tedious case of aqueous polymer dispersions where most of the thiocarbonylthio terminal group is buried into the core of the polymer particle. In this work, ozone is proposed to tackle this important academic and industrial challenge. After preliminary model ozonolysis reactions performed on a xanthate RAFT agent and a derived low molar mass poly(n-butyl acrylate) (PBA) in dichloromethane solution, it is shown that the hydrophobic nature and strong oxidant properties of ozone are responsible for its efficient diffusion in aqueous PBA latex particles obtained by RAFT and selective and complete transformation of the xanthate terminal group into a thiocarbonate end-group. In addition to the beneficial total discoloration of the final product, this chemical treatment does not generate any volatile organic compound and leaves the colloidal stability of the polymer particles unaffected, provided that a PBA latex with a sufficiently high Mn of 5000 g mol(-1) is selected.

Synthesis of clay-armored poly(vinylidene chloride-co-methyl acrylate) latexes by Pickering emulsion polymerization and their film-forming properties

We report the surfactant-free emulsion copolymerization of styrene (Sty)/methyl acrylate (MA) and vinylidene chloride (VDC)/MA by using clay platelets (LAPONITE® or a mixture of LAPONITE® and Montmorillonite) as Pickering stabilizers. Several parameters such as the presence of MA, the clay percentage and the monomer composition were shown to play a crucial role in the formation and stability of the resulting clay-armored particles. Optimal batch conditions led to stable latexes with a shelf life of at least one year. The film-forming process of the clay/P(VDC-co-MA) hybrid latexes was then studied. Transmission electron microscopy analysis of ultrathin cross-sections of the nanocomposite films revealed that latexes with high VDC contents (≥90 wt%) were not film-forming, whereas those of the same polymer composition but without clay led to a continuous film, suggesting that the clay platelets hindered polymer chain interdiffusion. Decreasing the VDC content to 87 wt% enhanced chain mobility, resulting in a uniform film with a honeycomb structure arising from the original clay-armored particle morphology.