Polymérisation par ouverture de cycle

thumb|Polymérisation par ouverture de cycle du caprolactame pour donner le polyamide 6. La polymérisation par ouverture de cycle (Ring-Opening Polymerization en anglais, soit ROP) est une polymérisation durant laquelle un monomère cyclique conduit à une unité monomère qui est acyclique ou contient moins de cycles que le monomère. Mécanismes Plusieurs mécanismes de polymérisation par ouverture de cycle existent :

le mécanisme cationique : le site actif de la chaîne de propagation est un carbocation ;
le mécanisme anionique : le site actif est un carbanion ;
le mécanisme par coordination-insertion, qui fait appel à un amorceur de type organométallique. Ce mécanisme implique la coordination de la liaison « C=O » à la liaison « C-atome métallique » de l’amorceur, suivie de l’insertion de cette même liaison au niveau de la liaison « oxygène-métal » par rupture de la liaison « C-O » endocyclique ;
le mécanisme organique, où l'amorceur est une espèce organique. Selon le m

Design of amphiphilic nanocapsules based on hyperbranched star-block copolymers for the encapsulation and the controlled release of olfactory compounds

Céline Ternat

Effective encapsulation of small, volatile, weakly water-soluble molecules such as flavors and fragrances is necessary to protect them from degradation, to increase their lifetime, and to improve their water dispersion and fixation depending on the substrate of interest. The aim of this project has been to improve encapsulation and release in order to optimize the performance of fragrance molecules in water-based household (detergents, softeners, etc.) and body care applications (shampoos, lotions, etc.), and fine perfumery applications. More specifically, the aim has been to investigate the effectiveness of "unimolecular micelles" based on amphiphilic multi-arm star-block copolymers with a hyperbranched core with more than 26 functional groups, a hydrophobic inner and a hydrophilic outer shell. These have been prepared from a commercial hyperbranched polyester macroinitiator (HBP) by ring-opening polymerization of ε-caprolactone, followed by the atom transfer radical polymerization (ATRP) of tert-butyl acrylate (tBuA). Hydrolysis of the tert-butyl groups has then been used to convert the poly(tBuA) blocks to poly(acrylic acid) (PAA), resulting in HBP-(PCL)p-(PAA)q pH-dependent amphiphilic star-block copolymers with good control of the molecular weight distribution. These were shown to form stable nanocapsules with a well defined core-shell architecture, as confirmed by thermal and microstructural characterization. The necessity of the core-shell architecture for the effective encapsulation of fragrance molecules in aqueous dispersion has been demonstrated by NMR (nuclear magnetic resonance). The extent of encapsulation reflects the dynamic equilibrium between the free molecules and the fragrance/polymer complex and is dependent on the octanol/water partition coefficient (logP) of the fragrance compounds, as demonstrated with a similar non ionic core-shell architecture HBP-(PBMA)37-(PPEGMA)39 composed of a hydrophobic poly(butyl methacrylate) (PBMA) core and a hydrophilic poly(polyethylene glycol) methyl ether methacrylate (PPEGMA) shell (provided by the Polymer Laboratory of the EPFL). The fragrance loadings in the polymer (HBP-(PCL)p-(PAA)q and HBP-(PBMA)37-(PPEGMA)39), which reached up to 30 wt% depending on the type of the fragrance molecule, were argued to be linked to their solubility in the hydrophobic core of the star-block copolymer. Moreover, under conditions representative of real applications (fine perfumery and softener applications) the star-block copolymers significantly extended the time over which the concentration of certain volatiles remained above the human olfactory threshold. Effective encapsulation and delayed release of small hydrophobic molecules was hence demonstrated to be possible with the present systems. The straightforward synthesis, tailorable chemistry and globular architecture of the star-block copolymers investigated here therefore offer promise for the development of relatively cheap encapsulants with affinities for specific components in fragrance packages, and release triggered by selected substrates according to their surface chemistry.

EPFL2007

Design, Synthesis and Characterization of New Nanoparticle Stabilizers and Their Application in Catalysis

Ilaria Biondi

In recent years, a strong emphasis in research towards creating sustainable and environmental friendly chemical processes has propelled the development of novel types of catalytic systems that combine advantages from homogeneous and heterogeneous processes. In this respect, transition metal based nanoparticles, TM-NPs, are excellent candidates with properties that offer high efficiency, high selectivity and the possibility of recycling. However, due to the particularly small size, within the nanoscale, TM-NPs are generally only kinetically stable and must be supported or stabilized by molecular systems to prevent aggregation into larger, less active materials. The work presented herein concerns the design, synthesis, characterisation and the applications of new TM-NP protecting agents, which are based on polymers functionalized with components that compose ionic liquids, P-ILs. Specifically, these P-ILs feature a hydrophobic poly-norbornene framework prepared using Ring Opening Metathesis Polymerization, ROMP, with pendant imidazolium-based ionic liquid substituents that allow fine tuning of the polymer solubility by anion-exchange. In Chapter 2, an aqueous, soluble P-IL containing the 1,2-dimethylimidazolium methane-sulphonate substituent and its use in the synthesis of aqueous gold NP, GNP, solutions is described. These particular TM-NPs were characterized by UV-VIS spectroscopy and Transmission Electron Microscopy, TEM. Subsequently, the P-IL/GNP solutions were used to catalyse the reduction of p-nitrophenol and the hydrogenation of cinnamaldehyde, both reactions are found to exhibit excellent activity under mild conditions. In Chapter 3, the potential of aqueous P-IL stabilizers to transfer GNPs from water to hydrophobic ILs and organic solvents is demonstrated. Using an anion-exchange process, the phase change does not result in GNP aggregation, as confirmed by UV-VIS spectroscopy and TEM analysis. Moreover, the same P-ILs were used as a protecting agents for the synthesis of aqueous rhodium NPs, RhNPs, which have been applied in the catalytic hydrogenation of natural compounds, including limonene, cinnamaldehyde, citral and α- and β-ionones. Through anion-exchange, the aqueous P-IL stabilized RhNPs are readily transferred into hydrophobic ILs, then used as catalysts in the hydrogenation of styrene and limonene. The stabilized RhNPs exhibited good activity, even after recycling. X-ray Photoelectron Spectroscopy, XPS, analysis demonstrated conclusively that the anion exchange and phase transfer of the Rh/Au-NP-IL system. In Chapter 4, three P-ILs containing poly-oxy linker groups, strategically placed between the poly-norbornene framework and the ionic groups, are described. The linkers provide additional stabilization through steric stabilization and coordination via the ether functional groups. These P-ILs were used to stabilize aqueous GNPs, which were characterized by UV-VIS spectroscopy and TEM. Their application in the reduction of p-nitrophenol reduction was demonstrated. Preliminary studies on the stabilization mode of PILs shown that the polymers, despite the presence of ionic groups, can stabilize electrostatically stabilized aqueous GNPs which otherwise aggregate in presence of water soluble imidazolium-based ILs. Moreover, they display good efficiency in terms of steric stabilization, comparable to systems featuring the poly-vinylpyrrolidone, PVP.

EPFL2011

Design of amphiphilic nanocapsules based on hyperbranched star-block copolymers for the encapsulation and the controlled release of olfactory compounds

Céline Ternat

EPFL2007

Design, Synthesis and Characterization of New Nanoparticle Stabilizers and Their Application in Catalysis

Ilaria Biondi

EPFL2011

Polymérisation par ouverture de cycle

Synthesis of cyclic (ethylene furanoate) oligomers via reactive distillation for ring opening polymerization

Design of amphiphilic nanocapsules based on hyperbranched star-block copolymers for the encapsulation and the controlled release of olfactory compounds

Design, Synthesis and Characterization of New Nanoparticle Stabilizers and Their Application in Catalysis

Design of amphiphilic nanocapsules based on hyperbranched star-block copolymers for the encapsulation and the controlled release of olfactory compounds

Design, Synthesis and Characterization of New Nanoparticle Stabilizers and Their Application in Catalysis

Synthesis of cyclic (ethylene furanoate) oligomers via reactive distillation for ring opening polymerization