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.

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.

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.

Polymer-grafted-platinum nanoparticles: from three-dimensional small-angle neutron scattering study to tunable two-dimensional array formation.

Nanohybrid objects based on polymer and platinum nanoparticles are of great interest for applications in fuel cells or as biosensors. The polymer part can help first to stabilize and to organize the particles, second to increase the amount of chemical functions available in the organic corona, and, finally, to improve or to mask the properties of the particles. The method to introduce the polymer consists of using both the "grafting from" technique and controlled radical polymerization (atom transfer radical polymerization). Small-angle neutron scattering (SANS) is a well-suited technique for the study of these objects, particularly due to the possibility to use contrast matching to see either the particle or the polymer corona. Polymerization kinetics was followed by SANS and the polymer corona spectra showed a plateau at small q which attested that the objects are individual and well-dispersed. These systems were exempt of free polymers, so the characterization via SANS could lead to quantitative data such as the radius of gyration of the object, the amount of grafted chains and the molecular weight of the chains, using a star model to fit the data. Langmuir films have then been obtained directly from the polymer-grafted-nanoparticles solutions, and compression isotherms have been recorded followed by transmission electron microscopy (TEM) characterization of the films at different pressures. A good correlation has therefore been observed from the distances between objects calculated using the compression isotherms or observed via TEM and the objects' dimensions determined from SANS study.