Sylvie Pourchet

Facile and efficient chemical functionalization of aliphatic polyesters by cross metathesis

An effective preparation of new tailor-made macromolecular materials via a combination of two (atom-efficient) catalytic transformations is reported. First, new aliphatic polyesters with alternated composition have been prepared using a salen aluminum catalyst system. Next, the pendant vinyl moieties in those copolymers have been selectively transformed into various functional groups by metathesis in the presence of homogeneous Grubbs catalysts. The latter metathesis reaction has been optimized in terms of catalytic activity and selectivity, to define the conditions for an effective and safe procedure that does not affect the macromolecular architecture. All polymer materials have been analyzed by 1H, and 13C NMR spectroscopy, to diagnose the catalyst selectivities in the copolymerization and metathesis processes.

Diglycidylether of iso-eugenol: a suitable lignin-derived synthon for epoxy thermoset applications

A novel lignin-based synthon, diglycidylether of iso-eugenol (DGE-isoEu) is used as a prepolymer for the preparation of thermosetting resins. DGE-isoEu is synthesized in a two-step procedure with a satisfactory yield from bio-based iso-eugenol (isoEu, 2-methoxy-4-(1-propenyl)phenol) catalytically fragmented from lignin in an organosolv process. DGE-isoEu was fully characterized by NMR, MS and FTIR. Curing of the DGE-isoEu monomer has then been investigated in the presence of several carboxylic acid derivatives hardeners. The thermal and mechanical properties of each material were recorded showing, in particular, a high Tg and instantaneous modulus values in the range of 78–120 °C and 4.6–5.5 GPa, respectively. The lignin derived new materials give very attractive thermo-mechanical properties comparable to that of common BPA-containing epoxy resins.

Influence of Three Types of Superplasticizers on Tricalciumaluminate Hydration in Presence of Gypsum

Different types of superplasticizers have been widely used over the past few decades in order to produce a more fluid or very high strength and durable concrete. These chemical admixtures interfere with the various physico-chemical processes occurring in early cement paste. In this paper we present results from a study on the influence of superplasticizers on pure tricalciumaluminate hydration in presence of gypsum. The suspensions hydration has been investigated by conductimetry, isothermal calorimetry and total organic carbon analysis of the liquid phase. The time taken for ettringite formation has been determined without superplasticizer and in presence of three different types of superplasticizers: polynaphtalene sulfonates (PNS), polycarboxylate-polyox (PCP) and diphosphonate terminated polyoxyethylene. Whereas diphosphonate terminated polyoxyethylene does not seem to modify tricalcium aluminate hydration carried out in presence of gypsum, PCP and even more PNS slow down ettringite formation. This effect seems to be largely due to a decrease of the C3A dissolution rate and might be connected to an adsorption of PCP. or PNS observed from the early C3A hydration. Such an adsorption does not happen with diphosphonate terminated polyoxyethylene superplasticizer. Moreover the presence of PCP superplasticizer causes a decrease in the size of the ettringite crystals formed.

Changes in Cement Paste and Mortar Fluidity after Mixing Induced by PCP: A Parametric Study

The interaction mechanism between polycarboxylate-type superplasticizer (PCP) and cement hydration is not fully understood and incompatibilities between concrete and additive are sometimes observed. In some cases, the fluidity tends to increase (“overfluidification”) few minutes after mixing. This is a problem because the overfluidification leds to bleeding of the concrete which could be critical on job site. Our study consisted first in highlighting the phenomenon of “over-fluidification” by slump flow tests on mortar. Next, the time evolution of the rheological behaviour of cement pastes in the presence of PCP was analysed thanks to a rheometry protocol in order to quantify the phenomenon. Later on, a parametric study was undertaken using this methodology. The operating conditions such as temperature and mixing process were studied as well as the effect of PCP structural parameters and the chemical characteristics of cement. In order to understand the origin of the phenomenon, adsorption measurements of PCP on cement particles were performed in the same conditions as those in the rheological measurements. Indeed, the phenomenon of “over-fluidification” could be related to the rate of the initial adsorption and the adsorption kinetics, both of which depend on the parameters of the process, the PCP structure and the cement reactivity.

Synthesis, characterization, and thermal properties of N,N,N′,N′-tetramethyl guanidinium tribromidocadmate(II) exhibiting an unusual coordination geometry

Abstract The reaction of N,N,N′,N′-tetramethyl guanidine, NHC(N(CH3)2)2 (TMGD) and CdBr2·4H2O in ethanol led to the formation of [TMGDH][CdBr3] (1), which crystallizes in the monoclinic space group Cc with Z=4, a=8.9079(7) Å, b=18.5810(14) Å, c=8.1637(6) Å, β=107.953(3)°, and V=1285.44(17) Å3. In the crystal lattice, 1 is organized in one-dimensional anionic chains of CdBr4 tetrahedra sharing two corners. To our knowledge, this is the first evidence of such a coordination geometry described for a bromocadmate derivative. The negative charges are compensated by monoprotonated N,N,N′,N′-tetramethyl guanidinium cations (TMGDHs), which are in N-H hydrogen bonding interaction with the terminal bromide atoms of the anionic chain. The title compound was also characterized by middle and far-infrared spectroscopy, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The elemental analysis corroborates as well the X-ray elucidation. Multinuclear solution nuclear magnetic resonance (NMR) spectroscopic measurements (1H, 13C{1H}) were conducted in D2O.

Crystal structure of the diglycidyl ether of eugenol

The diepoxy monomer (DGE-Eu) was synthesized from eugenol by a three-step reaction. It consists of a 1,2,4-trisubstituted benzene ring substituted by diglycidyl ether, a methoxy group and a methyloxirane group. The three-membered oxirane rings are inclined to the benzene ring by 61.0 (3) and 27.9 (3)°. In the crystal, molecules are linked by C—H⋯O hydrogen bonds, forming layers parallel to the ab plane.