Adsorption of PolyCarboxylate Poly(ethylene glycol) (PCP) esters on Montmorillonite (Mmt): effect of exchangeable cations (Na+, Mg2+ and Ca2+) and PCP molecular structure.

This study deals with the adsorption of PolyCarboxylate Poly(ethylene glycol) esters (PCP) superplasticizers on Na-, Mg- and Ca-saturated Montmorillonite (Mmt) clays. The interactions have been examined through different experimental methods: adsorption isotherms, zeta potential measurements and sedimentation experiments. It was found that PCP adsorption depends both on the architecture of PCP molecules and the nature of cation located on the interlayer exchange sites of the Montmorillonite. Whatever the PCP, a larger amount was adsorbed on Na-Mont than on Mg-Mont or Ca-Mont. This indicates the occurrence of two adsorption mechanisms: (i) a superficial adsorption via electrostatic interactions between the carboxylate groups of PCP and positively charged sites on clay surfaces, (ii) intercalation of ether units of the PCP grafts in the interlayer space by displacement of water molecules coordinated to the exchangeable cations. Furthermore, despite the weak negative values of the zeta potential, the addition of PCP promotes the stability of the suspensions which is attributed to steric repulsion acting between particles.

Synthesis of hybrid dendrimer-star polymers by the RAFT process.

A first generation phosphorus-containing dendrimer with twelve terminal benzyl dithiobenzoate functions was designed and subsequently used as a multifunctional agent to derive hybrid star copolymers consisting of a dendritic core surrounded by twelve polystyrene branches by reversible addition-fragmentation chain transfer (RAFT).

Giant dendrimer-like particles from nanolatexes.

A straightforward grafting of a polycationic phosphorus-containing dendritic shell onto polystyrene nanoparticles leads to dendronized nanoparticles showing unique behavior.

Thioacylation reactions for the surface functionalization of phosphorus-containing dendrimers.

The functionalization of phosphorus-containing dendrimers was easily achieved through thioacylation reactions involving new dendrimers capped with dithioester end groups and various functionalized amines. These reactions were successfully applied to the first generation (12 end groups) and the third generation of the dendrimer (48 end groups) and allowed their functionalization by various primary or secondary amines, alcohols, glycols, and azides. [reaction: see text]

Neodymium alkoxides: synthesis, characterization and their combinations with dialkylmagnesiums as unique systems for polymerization and block copolymerization of ethylene and methyl methacrylate.

The synthesis and characterization (NMR and X-ray) of a variety of neodymium alkoxides derived from simple and functionalized tertiary monoalcohols, and their application as inorganic precursors in combination with dialkylmagnesium reagents for ethylene and methyl methacrylate (MMA) (co)polymerization have been investigated. Salt metathesis reactions between NdCl(3) and sodium alkoxides in THF led to the formation of trinuclear complexes [Nd(3)(mu(3)-OR)(2)(mu(2)-OR)(3)(OR)(4)(thf)(2)] with R=tBu (1), tAm (2), while aggregate structure [Nd(12)(OtAm)(26)(HOtAm)(2)Cl(11)Na].(OEt(2))(2) (3) was obtained when the synthesis was performed in Et(2)O. [Nd(3)(mu(3)-OtBu)(2)(mu(2)-OtBu)(3)(OtBu)(4)(HOtBu)(2)] (4), prepared by aminolysis of Nd[N(SiMe(3))(2)](3) in hexane, slowly decomposed in toluene into oxo complex [Nd(5)(mu(5)-O)(mu(3)-OtBu)(4)(mu(2)-OtBu)(4)(OtBu)(5)] (5). Finally, the dimer [Nd(2)(mu(2),eta(2)-OR)(2)(eta(2)-OR)(2)(eta(1)-OR)(2)] (OR=OCMe(2)CH(2)CH(2)OMe) (6) was synthesised by aminolysis reaction from the corresponding gamma-donor-functionalized alcohol. Some of these neodymium alkoxides, in particular homoleptic complex 1, when associated in situ to one equivalent of a dialkylmagnesium, allow the formation of an active catalyst for ethylene polymerization. Under mild conditions (0 degrees C, 1 bar), the latter catalyst system exhibited a moderate activity (5-10 kg mol(-1) h(-1) bar(-1)). Effective transfer reactions were observed in the presence of H(2) or PhSiH(3) and renewal/improvement of activity occurred upon extra addition of dialkylmagnesium. The most outstanding feature of this catalytic system lies in the precipitation of the active "Nd-polyethylenyl" species during the ethylene polymerization course as solid S which could be isolated. This heterogeneity was turned to good account, enabling to achieve heterogeneous solid-gas ethylene polymerization and to prepare diblock PE-PMMA copolymers with high diblock efficiency and high molecular weights (M(n) > 200 000). A catalytic cycle for this unique system is proposed based on the isolation of a transmetallation product (7) from a neodymium alkoxide/dialkylmagnesium combination and NMR studies of the latter.