Jean-Michel Widmaier

Kinetics of formation of polyurethane-poly(methyl methacrylate) interpenetrating polymer networks: 2. Synthesis of the rigid network in the presence of the elastomeric network

Abstract The kinetic aspects of the formation of a second network in the presence of the first have been studied in polyurethane-poly(methyl methacrylate) interpenetrating networks. The effect on kinetics of parameters such as the polyurethane content, the amount of acrylic crosslinker and the reaction temperature has been examined. It was found that the elastomeric polyurethane acts as a diluent that allows complete conversion of the acrylic monomers, and, through its viscosity, induces gelation of the reaction medium at the very beginning of the polymerization.

Polydimethylsiloxane/poly(methyl methacrylate) interpenetrating polymer networks: 2. Synthesis and properties

Abstract The synthesis of full and graft interpenetrating polymer networks (IPNs) based on polydimethylsiloxane and poly(methyl methacrylate) is described. IPNs were obtained by an in-situ sequential synthesis. Most samples were opaque; however, in a few cases, transparency was noted. Other properties like stress-strain behaviour, hardness and glass transition temperature were examined. Owing to the particular behaviour of silicone-containing polymers, the surface properties and the permeability to oxygen of these IPNs were also studied.

Polystyrene-poly(α-methylstyrene) blends: Influence of molecular weight on miscibility

Abstract Blends of polystyrene of molecular weights from 4000 to 80000 g/mol with poly(α-methylstyrene) of molecular weights from 55000 to 300000 g/mol were made by freeze-drying from benzene solutions. Glass transition temperature measurements by differential scanning calorimetry indicate that the miscibility behaviour of the polymers is very sensitive to change of molecular weights. A decrease of polystyrene chain length changes a two-phase system into a miscible or partially miscible blend. Broadening of the transition region and temperature shifts suggest that the polystyrene dissolves more in the poly(α-methylstyrene) phase than does the poly(α-methylstyrene) in the polystyrene phase.

Polydimethylsiloxane/poly(methylmethacrylate) interpenetrating polymer networks: 1. Efficiency of stannous octoate as catalyst in the formation of polydimethylsiloxane networks in methyl methacrylate

Abstract Deactivation of the polycondensation catalyst in in situ sequential syntheses of polydimethylsiloxane/poly(methyl methacrylate) interpenetrating polymer networks was observed, which impeded the gelation of the elastomeric network. The loss of catalytic activity could be ascribed to the simultaneous presence of radicals and oxygen in the reaction medium. When either oxygen is excluded or a radical inhibitor added, the polycondensation proceeds to gelation at the expected rate.

Competition between polycondensation of α,ω-dihydroxy polydimethylsiloxane and its condensation with alkoxy silane: A kinetic approach

Abstract α,ω-Dihydroxy polydimethylsiloxane (PDMS) undergoes a linear polycondensation, catalysed by stannous octoate, which can yield high molecular weight species. In the presence of monoalkoxysilane, both a polycondensation and a blocking reaction take place simultaneously. Such a condensation between α,ω-difunctional PDMS chains may also occur in the case of crosslinking involving tri- or tetra- alkoxysilane. This implies that, in the so-called model networks thus formed, the average length of the elastic chains is definitely different from that of the precursor chains.

Thermal ageing of polyurethane with hydrogenated polyisoprene soft segments

Abstract Polyurethane elastomers based on 4,4′-diphenylmethane diisocyanate, hydrogenated hydroxy terminated polyisoprene (HHTPI) and 2-ethyl-l,3-hexane diol were prepared by the classical one-shot method and subjected to thermal ageing at 150 °C. From the changes in the infra-red spectra, glass transition temperature, dynamic viscoelasticity and mechanical properties, it has been concluded that these HHTPI based polyurethanes were more resistant to degradation than the corresponding unsaturated hydrocarbon (i.e. polybutadiene) based materials.

Effect of stannous octoate on the thermal decomposition of 2,2′‐azobis(isobutyronitrile)

The thermal decomposition rate constant kd of 2,2′-azobis(isobutyronitrile) (AIBN) in ethyl acetate was determined at 60 °C in the presence of various amounts of stannous octoate (SnOc2). The kd values were found to be dependent on the concentration of SnOc2 in the solution. This dependence is not a linear function of the concentration because kd goes through a maximum when [SnOc2]/[AIBN] = 1. These features were explained by assuming the formation of a 1:1 cyclic complex between the nitrile groups of AIBN and the tin atom of SnOc2. This complex induces steric constraints in the azo bond of AIBN, thus increasing its rate of decomposition. © 2000 Society of Chemical Industry

Influence of a metallic filler on polyurethane formation

The addition of metallic fillers is recognized to impart improvement of acoustic properties to polyurethane-based materials used for marine applications. The system under consideration was obtained by the reaction of a triisocyanate-terminated prepolymer with 1,4-butanediol, in the presence of various concentrations of lead powder. With increasing lead content, gelation time is reduced and an Einstein-type law does not apply. The kinetics of the reaction were determined by Fourier transform infrared spectroscopy. Deviation from the classic second order is observed for the filled systems, and the higher the lead content, the more important the deviation is, showing undoubtedly the catalytic effect of the metallic powder.

Linear polycondensation of α,ω-dihydroxy polydimethylsiloxane, catalyzed by stannous octoate

Abstract In the presence of stannous octoate, high molecular weight polydimethylsiloxane (PDMS) is obtained from an oligomeric α,ω-dihydroxy PDMS. The polycondensation reaction is limited by the presence of oxygen and/or water. Only linear species are found, and network formation has never been observed.

Relationships between polymerization activating systems and viscoelastic properties of the subsequent polyurethane/poly(tert‐butyl acrylate) interpenetrating polymer networks

To date, most interpenetrating polymer networks (IPNs) are developed for slow processes such as casting or coating. For industrial manufacturing, fast-reactive polymer processing is often required. Simply increasing the amount of catalyst and/or free-radical initiator shows some limitations. Also, increasing too much temperature may cause degradation or side reactions. For polyurethane/polyacrylate IPNs, more or less simultaneous formation of the two networks, with over 97% conversion was obtained after 4 to 6 min at 110°C, using appropriate catalyst/initiator combinations. Depending on the relative kinetics of network formation, either one, two, or multiple transitions were found for a given composition. Kinetics of formation and phase behavior have been investigated by Fourier transform infrared spectroscopy and dynamic mechanical analysis.