François Schué

New catalyst systems for the polymerization of acetylene

Abstract The catalytic activities of WCI6Ph4Sn, MoCl5Ph4Sn and tetrabenzyltitanium were examined in the polymerization of acetylene. The structure, morphology and electrical conductivity of the doped and non doped polyacetylene were also studied.

Modification of the biocompatible and haemocompatible properties of polymer substrates by plasma-deposited fluorocarbon coatings

The polymerization of gases present in a low temperature plasma is a technique particularly well suited for biomedical material processing. Therefore, the possibilities this technique offers to increase the biocompatibility and haemocompatibility of polysulphone and poly(hydroxybutyrate) membranes to be used in a new bioartificial pancreas device were studied. The deposition of thin fluorocarbon coatings from an argon plasma containing perfluorohexane gave very smooth and hydrophobic surfaces without affecting the filtering properties of the treated membranes. Adding hydrogen increased the reaction yield, but gave rougher and less hydrophobic coatings. We characterized the biological properties of the treated surfaces and discussed the influence of the modified surface properties on the biological behaviour of the treated polymers. The good biocompatibility of the deposited coatings was established by following in vitro the insulin secretion of Langerhans islets cultured on the treated membranes and by examining the fibrous capsule that developed on plasma-treated polymer disks after three months of in vivo incubation in the peritoneum of Wistar rats. Rough and haemocompatible films of poly(hydroxybutyrate) and smoother, but more thrombogenic, polysulphone films were treated by perfluorohexane and perfluorohexane + H2 plasmas to study the relative influence of surface roughness and surface energy on polymer thrombogenicity. In vitro protein adsorption and total blood clotting tests proved that the surface roughness influences the thrombogenicity more than the other surface properties. This study seems to show that the plasma deposition of smooth and hydrophobic fluorocarbon coatings can increase the biocompatibility and reduce the surface thrombogenicity of the treated membranes without affecting their filtering properties.

Polymerization of acetylene by soluble Ziegler-Natta catalyst. Kinetic studies

Abstract In the present work some preliminary studies on the kinetics and the optimum conditions for the preparation of polyacetylene films are reported using the soluble Ti(OC4H9)4Al(C2H5)3 system, as well as the observation of the morphology of the films by electron microscopy. The kinetic curves obtained show two distinct parts: a rapid consumption of acetylene, followed by a retarding of the rate due to the polyacetylene film formed. If the rate of polymerization is plotted as a function of ageing time of the catalyst for a ratio Al Ti = 4 , a maximum is found for about one hour.

Segmented network structures for the separation of water/ethanol mixtures by pervaporation.

α,ω-Acrylate terminated poly(1,3-dioxolane) (polyDXL), was used as a hydrophilic cross-linker of hydrophobic poly(methyl methacrylate) (polyMMA) chains for the synthesis of amphiphilic AB-block copolymer networks. The application of these segmented networks as membranes for dehydration of water/ethanol mixtures by the pervaporation technique was investigated. Because the cross-links inhibit to a great extent phase separation between the components of these materials, as revealed by dynamic mechanical thermal analysis, an optimal control of the membrane characteristics could be achieved by variation of the hydrophilicity–hydrophobicity balance and the cross-link density. The combination of desorption experiments, determination of swelling degrees and calculation of deviation coefficients (e) allowed us to demonstrate in these membranes the existence of a so-called coupling effect. It was shown that polyDXL plays a predominant role in the specific interactions between the membrane and the solvents, which cause the preferential water transport in all the membranes over the whole composition range of the feed mixture.

Sorption, diffusion and pervaporation of water/ethanol mixtures in polyetherimide membranes

Homogeneous and composite aromatic polyetherimide membranes were prepared by casting from N-methylpyrrolidinone (NMP) solutions and by electrodeposition of polymer at the cathode, respectively. The membranes were evaluated for their sorption, diffusion and pervaporation separation of water from ethanol with emphasis on the breaking of azeotropic composition. The membrane performance was shown to be dependent on the feed concentration, but still selective towards water over the whole composition range of the feed mixture. By looking at the surface energy parameters, the determination of degree of swelling and the calculation of deviation coefficients (epsilon), an interesting insight was gained into the coupling effect in this solvent/membrane system. From the sorption, diffusion and temperature-dependent permeation behaviour, it could be concluded that in this system the diffusivity of permeant plays a major role in determining the pervaporation performance, rather than the solubility.

Characterization and mechanical properties of water‐soluble poly(vinyl alcohol) grafted with lactic acid and glycolic acid

Poly(vinyl alcohol) (PVA), fully or partially hydrolyzed, was reacted with D,L-lactic acid and glycolic acid in different conditions to synthesize polymers with pendant lactate and glycolate groups. Various degrees of grafting were obtained. 1H- and 13C-NMR analysis as well as thermal and mechanical methods were used to characterize the polymers. Such grafts lead to polymers with lower glass transition temperature, therefor enhancing the polymers solubility in cold water (10°C) and improving flexibility and elasticity as well as tear resistance.

E.s.r. study of the Ti(OBu)4 catalyst mixture in silicone oil with regard to the synthesis of homogeneous and highly conducting (CH)x

Abstract E.s.r. spectra of a homogeneous catalyst system based on n -butyltitanate and triethylaluminium in a Al/Ti molar ratio of four were recorded in silicone oil at temperatures ranging from 22 – 130 °C. They contained signals with G values of 1.954, 1.972, 1.977, and 1.986, whose intensities varied with the ageing temperature. It is shown that increasing the catalyst ageing temperature above 100 °C favours only the active species with G value 1.954. This could be related to the initial rate of polymerization and to the synthesis of a more homogeneous, regular and highly conducting (CH) x film after doping with a 0.25 M FeCl 3 -nitromethane solution.

The electric breakdown behaviour of polyetherimide films

Polyetherimide is an amorphous thermoplastic resin with a high glass transition temperature. It is characterized by high heat resistance and mechanical properties, which make it suitable for industrial application. Two different polyetherimides (varying by chemical formula) were investigated, in terms of their dielectric strength and space charge behaviour. The comparison reveals important variations in the electric properties.

Characterization of plasma-treated poly (hydroxybutyrate) membrane surfaces by ESCA and contact angle measurements☆

Poly (hydroxybutyrate) membranes were used as substrates for cold plasma treatment with perfluorohexane. By varying a gas mixture of perfluorohexane and hydrogen, surface coatings of different hydrophobicity were obtained. In addition, inorganic glass slides were treated correspondingly. The plasma-treated samples were analyzed by ESCA with respect to the surface composition and by contact angle measurements with respect to the surface free energy. Atomic structures and surface energies of the deposited layers on the polymer substrates were compared to those on inorganic substrates. In both cases a strong correlation was found between the fluorine/carbon ratio as well as the oxygen/carbon ratio and the surface free energy. Furthermore, the plasma-treated membranes were investigated and characterized by their changed permeation properties in order to identify the influence of the surface coatings on the bulk properties. Up to a coating density of 50–100 γ/cm2 the filtration properties of the treated membranes remained unaffected.

Physical properties of polyacetylene films doped with MoCl5 and WCl6

Abstract The physical properties of polyacetylene (CH) x are considerably modified by doping with halogens ( p type) or alkalis ( n type). In this paper we present the effects of new kinds of dopants — salts of transition metals such as WCl 6 and MoCl 5 . Dopant diffusion inside the film, the electrical behaviour and the infra-red transmission are studied and compared with effects produced by usual dopants. They have low diffusion coefficients and readily produce large dopant concentration using salt solutions.