G. Stoclet

Isoprene–Styrene Chain Shuttling Copolymerization Mediated by a Lanthanide Half-Sandwich Complex and a Lanthanidocene: Straightforward Access to a New Type of Thermoplastic Elastomers†

A lanthanide half-sandwich complex and a ansa lanthanidocene have been assessed for isoprene-styrene chain shuttling copolymerization with n-butylethylmagnesium (BEM). In the presence of 1 equiv BEM, a fully amorphous multiblock microstructure of soft and hard segments is achieved. The microstructure consists of poly(isoprene-co-styrene) blocks, with hard blocks rich in styrene and soft blocks rich in isoprene. The composition of the blocks and the resulting glass transition temperatures (Tg ) can be easily modified by changing the feed and/or the relative amount of the catalysts, highlighting a new class of thermoplastic elastomers (TPEs) with tunable transition temperatures. The materials self-organize into nanostructures in the solid state.

Elaboration of poly(lactic acid)/halloysite nanocomposites by means of water assisted extrusion: structure, mechanical properties and fire performance

Poly(lactic acid) (PLA)/halloysite nanotube (HNT) nanocomposites were prepared using a water assisted extrusion process. Morphology, structure, thermomechanical properties and flame retardant properties of these nanocomposites were compared to those obtained in the case of nanocomposites obtained via the conventional extrusion process. Whatever the synthesis route used, mechanical tests indicate that HNTs have a reinforcing effect ascribed, at least partially, to the dispersion of the HNTs in the PLA matrix. Differential scanning calorimetry also shows that HNTs improve PLA crystallization and play the role of a nucleating agent. Moreover, cone calorimeter experiments show a drastic improvement in the reaction to fire of PLA when HNTs are added, especially at high filler content. This improvement arises from the fact that HNTs induce the formation of a protective inorganic layer at the surface of the sample. As the main results of this study, it has been shown that water assisted extrusion not only induced a better dispersion of the HNTs into the matrix but also that this process prevents polymer degradation during the extrusion. This unusual effect has been ascribed to a barrier effect of the water molecules that preferentially locate at the HNT–matrix interface. Even if not fully explained, it could be ascribed to a decrease in local shear levels (mechanochemical effect) and/or to a decrease in the catalytic effect of the HNT surface (chemical effect). Consequently this study reveals that water-assisted extrusion is a reliable route to prepare PLA/halloysite nanocomposites with enhanced properties.

Influence of fatty chain length and starch composition on structure and properties of fully substituted fatty acid starch esters

A series of almost fully substituted Fatty Acid Starch Esters (FASEs) has been obtained in a homogeneous LiCl/DMAc medium by grafting octanoyl (C8), lauroyl (C12) and palmitoyl (C16) chlorides onto 3 starch species: Amylo-Maize, Potato and Waxy Maize. Structure-property relationships of FASEs are investigated as a function of both fatty acid chain length and amylose/amylopectin ratio of the starch. The structural study has revealed a layered type organization in which starch chain planes are separated by fatty chains. The latter are interpenetrated and/or tilted for FASE-C16 whatever the origin of the starch is, and fatty chains partially crystallizes into a structure with hexagonal symmetry. FASEs with C8 and C12 side chains are totally amorphous. The mechanical behavior of FASEs is shown to depend on both side chain length and amylose/amylopectin ratio, and an increase in material ductility is observed at increasing amylose content for C8 and C12 side chains.

Influence of Processing Conditions on Morphological, Thermal and Degradative Behavior of Nanocomposites Based on Plasticized Poly(3-hydroxybutyrate) and Organo-Modified Clay

Abstract The effect of processing conditions (casting and extrusion) and plasticization on the disintegrability in compost of organically modified clay poly(3-hydroxybutyrate) nanocomposites was studied. Tributylhexadecylphosphonium bromide (TBHP) was used as organic modifier. As revealed by WAXS and TEM observations, intercalated nanobiocomposites with clay stacks and some individually dispersed platelets were obtained. The melting temperature of the neat PHB diminished with the addition of plasticizer, thus broadening the processing window. Biodegradation test revealed that while the clay slows down the degradation rate, the plasticizer increases the degradation of the samples, reaching a similar final percentage of disintegrability when both plasticizer and clay were added in the formulation.

Bottom-up synthesis of functionalized {Ce4(SiW9O34)2(L)2} polyoxometalates

The reaction of Na10[SiW9O34] with the 4f tetravalent cerium cation associated with four different organic O/N-donor ligands at pH = 4–4.5 gives rise to the formation of five anionic polyoxometalates [Ce4(μ3-O)2(SiW9O34)2(C4H5O4)2]10− (1), [Ce4(μ3-O)2(SiW9O34)2(C5H7O4)2]10− (2), [Ce4(μ3-O)2(SiW9O34)2(C5H8O2–NH3)2]8− (3), [Ce4(μ3-O)2(SiW9O34)2(C6H10O2–NH3)2]8− (4) and [(Ce3(μ3-O)(μ2-OH)3)(Ce6(μ3-O)4(μ3-OH)4)(SiW9O34)4]21− (5). Compounds 1–4 consist of one tetranuclear Ce-based cluster fragment stabilized by two [SiW9O34]10− polyanions and two organic linkers. Compound 5 is composed of a hexanuclear core combined with a trinuclear cerium core, stabilized by four [SiW9O34]10− moieties. The molecular species were characterized by single-crystal and powder X-ray diffraction, IR spectroscopy, TGA, SEM/EDX, SAXS and ICP analysis. The solution stability of compounds 1–4 was also assessed by 29Si and 183W NMR.

Processing of PVDF-based electroactive/ferroelectric films: importance of PMMA and cooling rate from the melt state on the crystallization of PVDF beta-crystals

Poly(vinylidene difluoride) (PVDF) displays attractive ferroelectric/piezoelectric properties and its polar β-crystals are specifically targeted for achieving electroactive applications. However, their direct crystallization from the melt state represents a challenging task that has never been addressed using melt-state processes. The use of poly(methyl methacrylate) (PMMA) is herein investigated to promote the PVDF polar β-phase using melt-blending and extrusion-calendering technologies. The presence of the β-phase is here confirmed by ATR-FTIR and WAXS experiments with blends at a PMMA content as low as 5 wt%. The key role of PMMA for the β-phase crystallization from the melt state was unambiguously highlighted with the help of Flash DSC experiments in non-isothermal cooling mode from the melt state. PMMA is able to efficiently shift the α-to-β crystal transition to lower cooling rates (>100-200 °C s-1), making the achievement of the PVDF polar β-phase for these blends compatible with conventional processing tools. A crystal phase diagram is proposed for the PVDF/PMMA blends to highlight the dual effects of both PMMA and cooling rate on the PVDF crystallization during melt-processing. Ferroelectric properties were even observed for the blends containing PMMA up to 10 wt% with the highest remanent polarization obtained at 5 wt% PMMA. After 10 wt% PMMA, a progressive transition from ferroelectric to pseudo-linear dielectric behavior is observed more likely due to the presence of PMMA in the interlamellar amorphous phase of the polar PVDF spherulites as shown by SAXS experiments. In this work, we successfully demonstrated that PMMA plays a key role in the crystallization of PVDF polar crystals from the melt state, enabling large-scale and continuous extrusion processing of PVDF-based materials with attractive dielectric properties for sensing and harvesting applications.

Complexation of tetravalent uranium cations by the As4W40O140 cryptand

The complexation properties of the anionic [As4W40O140]28− macrocycle were studied towards the trapping of the 5f tetravalent uranium tetrachloride precursor. In aqueous solution, the increase of the uranium concentration (from one to six molar equivalents per [As4W40O140] unit) leads to the crystallization of three new isolated crystalline compounds, [{U2(μ2-OH)3(μ2-O)}AsW40O140]25− (1), [{U2(μ2-O)(HCOO)3}As4W40O140]25− (2) and [{U4(μ2-O)2(HCOO)4}As4W40O140]20− (3), in which two to four uranium atoms were trapped within the cryptand-like molecule. In compounds 1 and 3, the macrocycle keeps its architecture, while a rotation of the position of one {AsW9O33} sub-unit of the cryptand could be observed in compound 2. All the inclusion complexes have been characterized by single-crystal X-ray diffraction, IR spectroscopy, TGA, SEM/EDX microscopy, SAXS and ICP analyses.

Synthesis and application of fatty acid derived templates for the preparation of mesostructured silica material

Bio-Organic-Salts (BOSs) synthesized from fatty acid methyl esters (FAMESs) have been developed for use as a bio-derived template for mesostructured material. Fatty acid derived imidazolium salts were prepared from very high oleic acid (VHOSO), linseed oil, and castor oil by a three-step synthesis involving transesterification, amidation and quaternisation. The as prepared BOSs were successfully applied as structuring agents for hexagonal mesoporous materials without necessity of hydrothermal treatment, as confirmed by TEM, SAXS and nitrogen physisorption.