Hubert Mutin

Organosilicon polymers: pyrolysis of poly[(silanylene)diethynylene]s

Abstract The pyrolysis of Si(CH 3 ) 2 Cue5fcCCue5fcC n in a stream of argon to 1400°C gives a SiC-containing ceramic in high yield (85%). TDA, TGA-mass spectrometry and solid state 13 C NMR studies are reported, and show that: (1) a low-temperature cross-linking process involving the diacetylenic units occurs at about 300°C below the mineralisation stage and (2) the weight decrease between 400°C and 800°C arises only from loss of H 2 , CH 4 and C 2 H 4 . Pyrolysis under NH 3 leads to Si 3 N 4 with loss of the carbon.

Organo-lined alumina surface from covalent attachment of alkylphosphonate chains in aqueous solution

The reaction of octylphosphonic acid with the surface of alumina nanoparticles has been investigated in order to prepare a close packing of grafted-alkyl chains. This goal was attained through a fitting selection of the experimental conditions in terms of pH, reactant amount, reaction time and temperature. DRX, TEM and 31P MAS NMR spectroscopy are all consistent with an efficient covalent anchorage of the alkylphosphonate chains without degradation of the support, demonstrated by the morphology and texture preservation during the modification. In addition to the textural analysis, nitrogen adsorption isotherms provide additional pieces of information on the interaction energy between the nitrogen molecule and the surface. These data, combined with those supplied by the empirical test of floatability of powders (methanol number test), as well as the adsorption properties of the differently functionalized alumina samples using other probes, such as hexane and water, as a function of the chain loading, provided converging information about surface coverage and the hydrophilic/hydrophobic properties of the various materials. Different conformations are proposed to take into account the different results obtained from vapor adsorption measurements.

Hybrid materials and silica: drastic control of surfaces and porosity of xerogels via ageing temperature, and influence of drying step on polycondensation at silicon

The effect of drying and ageing conditions on both the degree of polycondensation at silicon and the texture connected with the surface properties (BET, porosity) has been investigated in the case of silica and nanostructured hybrid organic–inorganic solids, obtained by hydrolytic sol–gel performed from a molecular precursor. Various molecular geometries and structural features were investigated using acid or nucleophilic catalysts in MeOH or THF. The aim of this work is first to study the effect of the temperature on the surface properties occurring during the ageing alone which was studied independently of gel formation. The second aim was to consider whether the polycondensation at silicon is influenced by the drying step. The main trend that emerges from these results is the drastic influence of ageing temperature on the texture and porosity of the xerogels. Whereas the level of condensation at silicon is not modified, we observed that higher ageing temperatures favor an increase of the specific surface area and an evolution towards a mesoporosity with narrow pore size distribution, whatever is the level of polycondensation at silicon. In contrast, the drying procedure (transformation of gel into xerogel) induces a significant increase of the level of condensation at silicon (10–14%) when the leaving group of the precursor is OEt, whereas in the case of the OMe group no evolution is observed. The same experimental facts have also been observed in the case of SiO2.

Novel aluminium phenyl, benzyl, and bromobenzylphosphonates: structural characterisation and hydration–dehydration reactions

Reaction of phosphonic acids RPO(OH)2 (R = phenyl, benzyl, 4-bromobenzyl) with aluminium nitrate and sulfate under various hydrothermal conditions led to three novel aluminium phosphonates, Al(OH)(O3PCH2C6H4Br)·H2O, Al(OH)(O3PCH2C6H5)·H2O and Al2(O3PC6H5)3·H2O. All the compounds were characterised by powder XRD, elemental analysis, TGA, 27Al and 31P MAS NMR and IR spectroscopy. The same tools were used to study the dehydration–rehydration reactions. Refinement of the structure of Al(OH)(O3PCH2C6H4Br)·H2O by the Rietveld method showed a lamellar arrangement similar to the methyl analogue ζ-Al(OH)(O3PCH3)·H2O. Al(OH)(O3PCH2C6H4Br)·H2O crystallises in the monoclinic system, space group P21/c with unit cell parameters a = 16.4972(2)xa0A, b = 7.0673(1)xa0A, c = 9.4950(2)xa0A and β = 113.477(1)°. Based on the powder XRD, IR and NMR data the two benzyl compounds were found to be isostructural.

A Catalytic Preparation of a New Preceramic Polymer: Transformation into SiC

The preparation of ceramic materials by organometallic processes has opened a new chapter in chemical research. In order to show the importance of the nature of the starting organometallic polymer, we have prepared a new ceramic precursor of the polycarbosilane type containing bifunctional silicon atoms. After characterisation of the nature and the structure of the units along the chains we obtained SiC ceramic via direct pyrolysis.