High Performance Polymers current issue

On the 70th Anniversary of the Birth of Marc J.M. Abadie

Bruma, M. — Wed, 14 Oct 2009 02:22:15 PDT

New Sulfonated Polyethers and Polynaphthylimides based on TNT Derivatives

Wed, 14 Oct 2009 02:22:15 PDT

New sulfonated and non-sulfonated monomers — dinitro and diamino compounds — were prepared on the basis of 1,3,5-trinitrobenzene (TNB) which is the demethylation product of 2,4,6-trinitrotoluene (TNT). The sulfonated dinitrocompounds interacted with different binuclear bis-phenols under the conditions of aromatic nucleophilic nitrodisplacement reactions. Polyethers of moderate molecular weights were prepared on the basis of dinitrocompound containing electron-withdrawing 3,5-dinitrodiphenyl sulfone-4'-sulfonic acid "bridging" groups. Copolymers and blends with other sulfonated polymers were prepared to improve the film-forming properties of the polyethers developed on the basis of 3,5-dinitrodiphenyl sulfone-4'-sulfonic acid. High molecular weight sulfonated polynaphthylimides were prepared by the interaction of sulfonated diamine containing electron-donating ether group — 3,5-diaminodiphenyl ether-4'-sulfonic acid — with bis(naphthalic anhydride)s. The sulfonated polyethers and polynaphthylimides thus obtained contain sulfonic acid groups in the side chains.

Comparative Study of Polyimides Containing Oxadiazole and Ether Groups

Bruma, M., Damaceanu, M. D., Muller, P. — Wed, 14 Oct 2009 02:22:15 PDT

An aromatic diamine with a preformed oxadiazole ring and various dianhydrides with ether and other flexible or bulky groups, such as isopropylidene, hexafluoroisopropylidene, cyclohexylidene or fluorenylidene, were used in a polycondensation reaction at high temperature to produce poly(oxadiazole-ether-imide)s. The properties of these polymers such as solubility, film-forming ability, thermal stability and photoluminescence were studied and compared with those of related conventional aromatic polyimides. The mechanical properties of the free-standing films obtained from these polyimides were also investigated.

Aromatic Polyethers based on Meta-activated Dinitrocompounds

Rusanov, A. L., Komarova, L. G. — Wed, 14 Oct 2009 02:22:15 PDT

Aromatic polyethers containing phenyl sulfone side groups were prepared using aromatic nucleophilic nitrosubstitution reaction. As starting compounds TNT-derived 3,5-dinitrodiphenyl sulfone and 4,4'-bis-[(3-nitro-5-phenylsulfonyl)phenylsulfonyl]diphenyl sulfone containing functional nitro groups activated with electron-withdrawing phenylsulfone meta-substituents were used. Polymers obtained are soluble in wide range of organic solvents and demonstrate large ‘windows’ between their softening and degradation temperatures.

Glycidoxypropylsilane-functionalized Magnetite as Precursor for Polymer-covered Core-shell Magnetic Particles

Wed, 14 Oct 2009 02:22:15 PDT

Surface-functionalized core-shell magnetic particles were obtained by reacting the hydroxyl groups on the surface of pre-prepared magnetite particles with 3-glycidoxypropyltrimethoxysilane. Fourier transform infrared spectra indicated that epoxy silane molecules were chemically bound onto the surface of magnetite particles through Fe—O—Si linkages. As proved by atomic force microscopy and environmental scanning microscopy combined with energy dispersive X-ray spectroscopy, particles with average core diameter and shell width of about 700 and 70 nm, respectively, were obtained. The covered magnetite particles showed a lower saturation magnetization (46 emu g¹) as compared to the uncoated magnetite (64 emu g¹).

Study of the Behavior of Some Polyheteroarylenes Treated with Supercritical Carbon Dioxide

Ronova, I. A., Nikitin, L. N., Sokolova, E. A., Sava, I., Bruma, M. — Wed, 14 Oct 2009 02:22:15 PDT

Various polyheteroarylenes have been studied with regard to their physical properties before and after treatment with supercritical carbon dioxide (sc-CO₂). Thus, the study of dependence of glass transition temperature and free volume of polymer matrix on the conformational rigidity showed that the process of swelling in sc-CO₂ is influenced by the residual solvent and by the formation of possible hydrogen bonds between CO₂ and amide groups in the polymer chain.

Copolymers Obtained by {epsilon}-Caprolactam and Methyl Methacrylate Polymerization in the Presence of Polyimides

Wed, 14 Oct 2009 02:22:15 PDT

New copolymers have been synthesized by anionic or radical photopolymerization of -caprolactam or methyl methacrylate (MMA) in the presence of dissolved polyimides bearing hexafluoroisopropylidene, fluorene or other groups. Using diimides as models it was shown that the kinetics of anionic polymerization of -caprolactam depends on the nature of spacer between the imide cycles. The mechanical and tribological properties of copolymers, their water absorbance and the microstructure of copolymer films were studied. It was found that upon the selection of polyimide activator it was possible to gain the desirable control over the polymer properties, namely, the gel fraction content, phase composition, compression modulus, notched Izod impact strength, friction coefficient and temperature of frictional contact. The kinetics of radical polymerization of MMA in the presence of polyimide and model diimide has been studied by differential scanning photocalorimetry and infrared spectroscopy. From the results of the reaction kinetics and the study of polymer structures by Fourier transform infrared spectroscopy, nuclear magnetic resonance, size-exclusion chromatography and thermogravimetric analysis it has been established that radical photopolymerization of MMA in the presence of polyimide leads to the formation of copolymers owing to chain transfer reactions and/or chain termination by the relevant condensation polymer. It has been established that the imide cycles play a significant role in the formation of both copolymers with -caprolactam and MMA, respectively.

Poly[( N-Acylimino)ethylene] Derivatives for Advanced Materials

David, G., Simionescu, B. C. — Wed, 14 Oct 2009 02:22:15 PDT

New segmented polyurethanes containing soft and hard segments of different polarity and hydrophilicity, based on 4,4^'-methylenebis-(cyclohexyl isocyanate, 4,4^'-methylenebis-(phenyl isocyanate) and poly(tetramethylene oxide) or poly(ethylene oxide) were prepared including poly[(N-acylimino) ethylene] sequences as a chain extender. They were comparatively characterized by spectral, thermal and mechanical techniques. Some preliminary investigations on their nanocomposites with montmorillonite as an inorganic component are presented.

Dynamic Mechanical Analysis of Polyurethane-Epoxy Interpenetrating Polymer Networks

Cristea, M., Ibanescu, S., Cascaval, C. N., Rosu, D. — Wed, 14 Oct 2009 02:22:15 PDT

A series of semi-interpenetrated polymer networks based on bisphenol A epoxy resin and polyurethane was synthesized by sequential procedure. The molecular dynamics of polyurethane incorporated in the resin network with increasing amounts of resin was followed by dynamic mechanical analysis. All phenomena that concur in the material are evaluated by cross-examination of the storage modulus (E'), loss modulus (E'') and loss factor (tan ) variation with temperature. Complex aspects were elucidated in consecutive heating-cooling-heating cycles and by calculating the apparent activation energy of relaxations in multiplex experiments.

Mechanistic Aspects of Polynaphthalimide Synthesis from NMR Analysis

Piroux, F., Mercier, R., Picq, D. — Wed, 14 Oct 2009 02:22:15 PDT

The mechanism of the polycondensation reaction leading to naphthalimide polymers has been investigated using a model compound. In complement to ¹⁹F-NMR analysis, ¹H- and ¹³C-NMR spectroscopies were used to identify the intermediate compound. It was concluded that there was no evidence for the formation of an isoimide, but the formation of an amide—acid intermediate was clearly demonstrated.

Aspects of Morphology Control during the Oxidative Synthesis of Electrically Conducting Polymers

Schulz, B., Dietzel, B., Orgzall, I., Diez, I., Xu, C. — Wed, 14 Oct 2009 02:22:15 PDT

The formation of micro- and nanostructures during the oxidative polymerization of polypyrrole and polyaniline is investigated using different sulfonic acid dopants. Rod- or tube-like structures are found in polypyrrole as well as in polyaniline without addition of further compounds to the initial reaction mixture of monomer, dopant and oxidant. In these cases, always a crystalline precursor complex composed of a dopand molecule and the pure monomer (aniline) or a trimeric moiety (pyrrole) serves as in-situ template. In most cases the surface of the growing polymer is covered by secondary structures with much smaller sizes so that a hierarchical order of structures at different length scales results. Corresponding model considerations for the polymerization process are outlined. Additionally, unusual structures like platelets, frames, rings, or ribbons are observed in the polypyrrole synthesis in the presence of fluorosurfactants.

High Temperature VARTM of Phenylethynyl Terminated Imides

Wed, 14 Oct 2009 02:22:15 PDT

Depending on the part type and quantity, fabrication of composite structures using vacuum-assisted resin transfer molding (VARTM) can be more affordable than conventional autoclave techniques. Recent efforts have focused on adapting VARTM for the fabrication of high temperature composites. Due to their low melt viscosity and long melt stability, certain phenylethynyl terminated imides (PETI) can be processed into composites using high temperature VARTM (HT-VARTM). However, one of the disadvantages of the current HT-VARTM resin systems has been the high porosity of the resultant composites. For aerospace applications, the desired void fraction of less than 2% has not yet been achieved. In the current study, two PETI resins, LaRC PETI-330 and LaRC PETI-8 have been used to make test specimens using HT-VARTM. The resins were infused into ten layers of IM7-6K carbon fiber 5-harness satin fabric at 260 or 280 ^°C and cured at temperature up to 371 °C. Initial runs yielded composites with high void content, typically greater than 7% by weight. A thermogravimetric-mass spectroscopic study was conducted to determine the source of volatiles leading to high porosity. It was determined that under the thermal cycle used for laminate fabrication, the phenylethynyl endcap was undergoing degradation leading to volatile evolution. This finding was unexpected as high quality composite laminates have been fabricated under higher pressures using these resin systems. The amount of weight loss experienced during the thermal cycle was only about 1% by weight, but this led to a significant amount of volatiles in a closed system. By modifying the thermal cycle used in laminate fabrication, the void content was significantly reduced (typically ~ 3% or less). The results of this work are presented herein.

Polysulfone-based Ionomers for Fuel Cell Applications

Iojoiu, C., Sanchez, J.-Y. — Wed, 14 Oct 2009 02:22:15 PDT

This paper is a review that is focused on ionomers based on aromatic polysulfone backbone and intended to be used in proton exchange membrane fuel cells or in direct methanol fuel cells. Emphasis is placed on the different chemical routes to prepare the ionomers. Special attention is given to the impact of the ionomer structure on the conductivity performance and on the dimensional stability of the membranes at high temperatures.