This article reports the synthesis of atom transfer radical polymerization (ATRP) of active initiators from well-defined silica nanoparticles and the use of these ATRP initiators in the grafting of poly(n-butyl acrylate) from the silica particle surface. ATRP does not require difficult synthetic conditions, and the process can be carried out in standard solvents in which the nanoparticles are suspended. This "grafting from" method ensures the covalent binding of all polymer chains to the nanoparticles because polymerization is initiated from moieties previously bound to the surface. Model reactions were first carried out to account for possible polymerization in diluted conditions as it was required to ensure the suspension stability. The use of n-butyl acrylate as the monomer permits one to obtain nanocomposites with a hard core and a soft shell where film formation is facilitated. Characterization of the polymer-grafted silica was done from NMR and Fourier transform infrared spectroscopies, dynamic light scattering, and DSC.

Polymer chains are grafted from silica beads (colloidal sol in dimethylacetamide) by atom transfer radical polymerization (ATRP). The method consists of grafting first the initiator molecules on the silica surface (“grafting from” method), in two steps. First, thiol-functionalization of the surface was achieved via silanization with a mercaptopropyl triethoxysilane. Second, we performed an overgrafting of the surface by reacting the thiol with 2-bromoisobutyryl bromide to generate the halogen-functional ATRP initiator. From that, the polymerization of styrene was conducted. Control of both the molecular weight and the density of grafted chains can be achieved by this method. The other originality of this work is that we keep the nanoparticles in solution at each stage of the procedure (even during the purification steps), as this is the only way to avoid irreversible aggregation. The state of dispersion of the grafted nanoparticles is followed by small-angle neutron scattering. Characterizations such as gel permeation chromatography, 29Si CP/MAS NMR, elemental analysis, infrared spectroscopy, and thermogravimetric analysis are conducted to confirm the success of the grafting reaction.

The first examples of reductive depolymerization of lignin are reported under metal-free conditions. Using hydrosilanes as reductants and B(C 6 F 5 ) 3 as a Lewis acidic catalyst, wood lignin is efficiently converted to a narrow distribution of phenol derivatives, at room temperature. A three-step methodology based on the selection of the wood species and the lignin extraction method, followed by a convergent reductive depolymerization enables the production of four structurally defined aromatic compounds. The phenol products were successfully isolated in 7 to 24 wt% yield from lignin and 0.5 to 2.4 wt% yield from wood. The strategy is found robust and is applied to 15 different wood plants, including gymnosperm and angiosperm species. The efficiency of this novel methodology has been evaluated based on spectroscopic characterization of the lignin preparations and isolated yields of mono-aromatic products.

The coordination−insertion ring-opening polymerization of ε-caprolactone was initiated from amine or hydroxyl groups spread over the surface of silica (ca. 30 nm) or cadmium sulfide (ca. 1.5 nm) nanoparticles, respectively. The initiation selectively occurred from the surface functional groups after activation into aluminum alkoxides species. The covalent grafting of the polyester chains was confirmed by the solubilization of the nanoparticles in organic solvents, e.g., CHCl3 and THF for silica nanoparticles and toluene for CdS nanoparticles, at least when the surface-grafted PCL chains were long enough. In the case of silica nanoparticles, the linear dependence of the PCL molar mass as determined by 1H NMR analysis on the initial monomer-to-amine ratio confirmed the controlled character of the polymerization. Transmission electron microscopy of thin films of PCL-grafted CdS revealed an homogeneous dispersion of the semiconducting nanoparticles throughout the polyester matrix.

Nanosized CdS clusters have been synthesized using polyester chains with a thiol end group as a covalently attached colloidal stabilizer. Clusters were grown through the reaction of thiourea with cadmium acetate, which was in competition with surface stabilization due to the tethered poly(caprolactone) (PCL) chains. The kinetics of the CdS cluster growth in the presence of poly(caprolactone) ligands were compared with those obtained using a low molecular weight thiol. Control of the particle size was also achieved by varying the ratio of thiourea to PCL ligands. The resulting nanoscopic entities obtained in different solvents (DMF or THF), remained stable in solution for several months and could be cast into films. Homogeneous dispersions of CdS particles in a polymer matrix were obtained by solvent evaporation. The particle size and distribution were characterized using ultraviolet-visible and photoluminescence spectroscopies, and transmission electron microscopy.

We report here two different methods for preparing thiol-functional polymers. The first method consists of esterifying the hydroxyl-terminated polyesters with a thiol-protected mercaptoacetic acid. The Sangers reagent (2,4-dinitrofluorobenzene) was used to protect the mercaptoacetic acid and was removed with mercaptoethanol under mild conditions. The second technique involves the preparation of a protected thiol-functional initiator, the α-(2,4-dinitrophenylthio)ethanol, that could then be used in the polymerization of ε-caprolactone. This “functionalization from initiation” technique could also lead to the preparation of well-defined multibranched polymers with a thiol group at the focal point after the polymerization with a mercapto-initiator carrying dihydroxy or tetrahydroxy functionalities as initiating sites. The ultimate motivation in the preparation of such functional polymers is to elaborate nanocomposites by using the polymers as macroligands in the synthesis of nanoparticles.

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Stable dispersions of anisotropic particles with nanometer dimensions can be prepared in a selective solvent through co-crystallization (stereocomplexation) between two enantiomeric-poly(lactide) block copolymers: poly(L-lactide)-poly(e-caprolactone) and poly(D-lactide)-poly(e-caprolactone). In the conditions of the experiment, no unspecific aggregation of the homochiral polylactide blocks occurs. 2 The only driving force for self-assembly is between PLLA and PDLA. The good colloidal stability of the dispersion, makes it possible to study the evolution of the particle shape and dimensions with time. The formation of these highly anisotropic particles was studied by a combination of techniques (infrared spectroscopy, light scattering, small angle neutron scattering and atomic force microscopy).