Michel Fontanille

Carbene complexes in organic synthesis: a new tungstacarbene-promoted alkyne insertion–olefin cyclopropanation reaction

Carbene complexes of tungsten, bearing a co-ordinated double bond two carbons away from the carbene function, react with alkynes to give, after insertion of the alkyne, bicyclo[4.1.0]heptane derivatives as a result of cyclopropanation of the double bond by the newly formed carbene complex.

Etude de la reactivite de la vinyl-2 pyridine en polymerisation anionique–II. Copolymerisation avec le diphenyl-1,1 ethylene

A kinetic study was made for addition of 1,1-diphenylethylene to active species-involved in anionic polymerizations of 2-vinyl pyridine and styrene in tetrahydrofuran solution with Cs+ as counter-ion: it showed that poly(styrene)− free ion is much more reactive than poly(2-vinylpyridine)− free ion. The intrinsic reactivity of the corresponding ion pairs varies in the same way as for the free ions but not proportionally. The measured values corroborate previous values established for the homopolymerizations of these monomers. For Na+ as counter-ion, the experimental results are explained by cation solvation by pyridine moieties.

The anionic bulk polymerization of α-methylstyrene-II. Kinetic study of the propagation

Abstract A kinetic study of the anionic bulk polymerization of α-methylstyrene initiated with tert-butyllithium (t-BuLi) in presence of N,N,N′,N′-tetramethylethylenediamine (TMEDA) has been performed. Kinetic measurements have been carried out using dilatometry at 25° and 40° up to 37% conversion. The reactivity of the system is found to be a function of the ratio r = [TMEDA]/[t-BuLi]. The apparent rate constant decreases with increasing values of r for r 1. The results are explained by the presence of three different active species, viz. contact ion-pairs contact ion-pairs stretched solvated with a TMEDA molecule, ion-pairs stretched by nTMEDA molecules. When the temperature is raised to 62°, the active centres become unstable and cyclic oligomers are formed.

Homogeneous epoxy-acrylic interpenetrating polymer networks: preparation and thermal properties

SummaryThe simultaneous interpenetration of two networks, one based on diglycidyl ether of bisphenol A crosslinked by an aliphatic diamine and the other one based on diglycidyl ether of bisphenol A dimethacrylate, leads to systems transparent to visible light. The measurement of glass transition temperature of these IPNs as a function of the composition and of the crosslinks density, gives relatively low and single values. This behavior is interpreted by the homogeneous structure of these systems.

Kinetic study of anionic polymerization of butadiene in a polar solvent

The kinetics of the propagation reaction for the polymerization of butadiene initiated by cumyl potassium in tetrahydrofuran solution at several temperatures have been studied. Kinetic data and electrolytic behaviour indicate that polybutadienyl free ions assume the whole of the propagation reaction. At 0°C, the respective rate constants for ion-pairs and free ions are 1 l mol−1 s−1 and 4.8 × 104 l mol−1 s−1 respectively. The ionic dissociation constant is 7.8 × 10−9 mol/l. The activation energy of the propagation reaction for free ions is 6.5 kcal/mol.

Polymerization of Alkynes Initiated by Stable Metal Carbene Complexes

The polymerization of alkynes (1-heptyne in particular) initiated by a transition metal carbene complex has been studied in detail from a kinetic and structural point of view.

Some thermal and rheological properties of homogeneous interpenetrating polymer networks

SummaryHomogeneous interpenetrating polymer networks, (IPNs), consisting of methacrylic and epoxy networks, were obtained at various compositions from a simultaneous polymerization of DGEBAMA and DGEBA. For each composition, the glass transition occurs at a well-defined temperature which is lower than the weighted average of the glass transition temperatures of each component. Tensile experiments showed a change of mechanical behaviour above some critical strain value. This phenomenon was corroborated by stress relaxation tests which allowed the determination of a complete relaxation below a critical strain. This strain is increasing with the temperature and decreasing with the crosslink density. Such a property disappeared after the addition of grafting molecules which prevented both networks from any relative sliding. In this way this behaviour appears to be a specific property of interpenetrating networks.ZusammenfassungHomogene, einander durchdringende Polymernetzwerke (IPNs), die aus Methacryl- und Epoxyd-Netzwerken aufgebaut sind, werden durch simultane Polymerisation aus DGEBAMA und DGEBA in verschiedenen Mischungsverhältnissen hergestellt. Für jede Zusammensetzung findet man eine wohldefinierte Glasübergangstemperatur, die niedriger ist als das gewichtete Mittel der betreffenden Temperaturen der Komponenten. Zugversuche zeigen eine Änderung des mechanischen Verhaltens oberhalb eines kritischen Wertes der Dehnung. Dieses Phänomen wird noch durch Spannungsrelaxationsmessungen erhärtet, bei denen unterhalb der kritischen Dehnung eine vollständige Relaxation beobachtet werden kann. Der kritische Dehnungswert steigt dabei mit der Temperatur und fällt mit der Vernetzungsdichte. Dieser Effekt verschwindet nach Zugabe von Pfropfmolekülen, die das Gegeneinandergleiten der Netzwerke verhindern, und erweist sich somit als eine spezifische Eigenschaft von einander durchdringenden Netzwerken.

Kinetics and Thermodynamics of Anionic Polymerization of 2-Isopropenyl Pyridine in Toluene

The thermodynamics and kinetics of anionic vinyl polymerization has been the subject of several investigations over the last few decades. [1–9] Of these, the anionic polymerization of alpha-substituted vinyl monomers [3–9] was most readily studied because of their relatively low ceiling temperature. In these studies, both the polymerization rate constants and equilibrium constants have been determined but the rate of depolymerization has not been measured directly, due to a number of reasons such as the lack of stability of the propagating carbanions and the rapid rates of depolymerization under conditions of interest. We now wish to report the direct determination of both the rates of polymerization and depolymerization of 2-isopropenyl pyridine (2-IP) in toluene with Li+ as counter-ion, and the comparison of the thermodynamic results with the kinetic data.