Michèle Schappacher

Controlled ring-opening polymerization of lactones and lactides initiated by lanthanum isopropoxide, 1. General aspects and kinetics

Ring-opening polymerization of various lactones and lactides initiated by lanthanum isopropoxide has been investigated. Analysis of molecular weights and molecular-weight distributions of the resulting polymers shows that the ring-opening process is a controlled reaction, which is initiated by a variable number of isopropoxy groups. This number depends on both the monomer and the [monomer]/[initiator] ratio. Kinetic studies indicate that all the polymerizations are equilibrated, and the corresponding thermodynamic parameters and the equilibrium monomer concentrations have been calculated. Comprehensive kinetics carried out for e-caprolactone abd δ-valerolactone polymerizations allows the determination of kinetic order relative to both monomer and initiator concentrations, along with that of the apparent rate constants of polymerization. It is also demonstrated that propagation occurs on aggregated (δ-valerolactone) or unaggregated (e-caprolactone) active polymer chains and that the ring-opening process proceeds via [O-acyl] bond cleavages.

Glycolipids as a source of polyols for the design of original linear and cross-linked polyurethanes

Two novel sugar-based fatty ester polyols were synthesized by selective transesterification of epoxidized methyl or ethyl oleate with unprotected methyl α-D-glucopyranoside and sucrose respectively, followed by hydrolysis of the epoxide moiety. The so-formed polyols were then used as polyurethane (PU) precursors in the polyaddition with isophorone diisocyanate (IPDI) in the presence of dibutyl tin dilaurate (DBTDL) as a catalyst. Interestingly, the reactivity of the hydroxyl functions attached to the sugar and to the fatty ester chain moieties respectively could be discriminated with respect to the solvent used, enabling the synthesis of either linear or cross-linked PUs. The linear PUs were studied by means of FTIR, 1H NMR spectroscopy and size exclusion chromatography, SEC. The thermo-mechanical properties of these original PUs bearing pendant or intramolecular sugar units were also analyzed by differential scanning calorimetry, DSC.

New cyclodisilazane monomers

Abstract N,N′-Dimethylcyclodisilazanes -SiMeRNMeSiMeR′NMe- , (R = R′= Me, Vi, or Et and R = Me, R′= Vi, Et, or Ph where Vi = vinyl) have been prepared in good yield by cyclization of bis(methylamino)silanes with chlorosilanes. 1 H, 13 C, 29 Si and 15 N NMR spectra have been assigned. The four-membered cyclic structure of the compounds have been confirmed by mass spectrometry and IR absorption measurements.