Water uptake and proton conductivity as a function of temperature were determined for three aromatic‐based, sulfonic acid‐bearing polymers, plus the perfluoroalkyl sulfonic acid Nafion® 117. Water uptake of submerged, equilibrated samples ranged from less than five water molecules per acid group for a high equivalent weight, sulfonated polyethersulfone to almost fifty waters per acid for a low equivalent weight, sulfonated polyetheretherketone. The most conductive aromatic‐based polymer, sulfonated polyphenylquinoxaline (S‐PPQ), had a room temperature conductivity of 9.8×10−3S/normalcm . about an order of magnitude less than that of a perfluoroalkyl sulfonic acid under identical conditions. The slope of the S‐PPQ Arrhenius conductivity plot was sufficiently steep that at 180°C, the proton conductivity, 1.3×10−1S/normalcm , was only a factor of two lower than that of Nafion under similar conditions. The lower conductivity of the aromatic‐based sulfonic acid polymers can be attributed to chain rigidity, lack of ion channels, and lower acidity. © 2000 The Electrochemical Society. All rights reserved.

Polymethylmethacrylate (PMMA)/silica nanocomposites are prepared by solution polymerization in this project and the resulting materials are subjected to characterization to evaluate thermal, mechanical, and fire properties. IR results show that both (3-acryloxypropyl)methydimethoxysilane (APMDMOS) and (3-acryloxypropyl)trimethoxysilane (APTMOS) can serve as reagents for the surface modification of silica, while APTMOS performed better than APMDMOS for the modification of the silica surface. Mechanical properties of PMMA/silica nanocomposites prepared by solution blending showed decreased tensile strength and elongation at break, while materials from solution polymerization performed better than PMMA itself. Moreover, all prepared samples have shown improved thermal stabilities versus PMMA. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3844 -3850, 2004

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Activity at the NASA Langley Research Center (LaRC) has focused on developing low density polyimide foam and foam structures which are made using monomeric solutions or salt solutions formed from the reaction of a dianhydride and diamine dissolved in a mixture of foaming agents and alkyl alcohol at room temperature. Monomer blends may be used to make a variety of polyimide foams with varying properties. The first foaming process developed consisted of thermal cycling the polymer precursor residuum and allowing the inflation of the particles to interact to create the foam. This process has resulted in foam structures with higher percentages of open cell content. Another innovative foaming process has been developed that begins with partially inflated microspheres, “friable balloons”, with incomplete polymer molecular weight gain, which when fully cured into a foam results in more closed cell structures. In a research study performed by NASA Kennedy Space Center (KSC) and LaRC, two closely related polyimide foams, TEEK‐H series and TEEK‐L series, (4,4′‐oxydiphthalic anhydride/3,4′‐oxydianiline and 3,3′,4,4′‐benzophenonetetracarboxylic acid dianhydride/4,4′‐oxydianiline) were investigated for density effects and closed versus open cell effects on the thermal, mechanical, and flammability properties. Thermal conductivity data under the full range of vacuum pressures indicate that these materials are effective insulators under cryogenic conditions. Contributing factors such as cell content, density, and surface area were studied to determine the effects on thermal conductivity. Cone calorimetry data indicated decreased peak heat release rates for the closed cell system, TEEK‐H friable balloons, compared to the TEEK foams with higher open cell content. Mechanical properties including tensile strength and compressive strength indicated that the materials have good structural integrity. Foams with more open cell content resulted in greater tensile and compressive strengths than the closed cell foams. The maximum closed cell content achieved in the “friable balloon” system was 78% at a foam density of 0.048 gm/cm3. Published in 2005 by John Wiley & Sons, Ltd.

Three polymer/silica nanocomposites were prepared by a single‐screw extrusion approach: poly(methyl methacrylate), polystyrene and polycarbonate/silica nanocomposites. The resulting nanocomposites were subjected to comprehensive studies of mechanical, thermal and flammability properties. All materials showed improved mechanical performance and thermal stabilities, although they are not strictly flame retardant when subjected to fire tests like Oxygen Index or horizontal Bunsen burner tests. However, the nanocomposites showed reduction in peak heat release rates and total heat release when evaluated by cone calorimetry. Moreover, the polycarbonate showed improvement in flammability according to vertical burning tests. All polycarbonate materials subjected to vertical burning testing are V2 rated, but after flame times with 1% silica were significantly reduced. A flame retardant mechanism is proposed in order to understand the relationship between interfacial interaction and flammability of polymer/silica nanocomposites. Copyright © 2006 John Wiley & Sons, Ltd.

No abstract

13C chemical shifts of phenyl ring carbons in substituted benzenes can be used to monitor changes in charge distribution at those carbons. Strong solute-solvent interactions such as hydrogen bonding to basic substituents result in significant changes in ring carbon chemical shifts. The changes in 13C shifts are related to the electronic perturbation of the substituent and the ring system in a near quantitative manner.Studies of these solvation effects in relatively dilute solution are facilitated by the use of Fourier transform (FT) techniques. Dilution curves indicate that for groups such as -OCH3 or -COCH3 in CF3COOH, a 10-15 mol % solute concentration effectively simulates infinite dilution insofar as electronic perturbation of the solute is concerned. By use of para 13C resonances, estimates of + values can be obtained for most substituents in most media.n contrast to the extensive investigation of solvent effects on proton chemical shifts, much less attention has been paid to the effects of solvents on 13C chemical shifts. Solvent dependence of the 13C chemical shifts of methyl iodide,2 acetonitrile,2 and chloro-form3 has been reported. Extensive solvent studies have been made on 13C resonances of carbonyl carbons,4-6 which were more easily observable by the 13C instrumental methods of the early 1960's. The carbonyl carbon of acetone, for example, shows a 13C chemical shift range of some 40 ppm over a variety of solvents.4 Surprisingly little work, however, has been reported on the effect of solvents on 13C chemical shifts of substituted aromatic systems. Some work relative to the effect of solvents on the 13C chemical shifts of phenol,7 benzonitrile,8 ,/V,iV-dialkylanilines,9 and acetophenones10 has been reported. Other than

The acetolyses of 3-substituted cyclobutyl tosylates (X = Ar, C1, and OEt) were examined giving rate constants and product distributions. With the alkyl-and aryl-substituted compounds, the rate-determining step leads to the formation of a bridged cyclobutyl cation which then rearranges to a cyclopropylcarbinyl/homoallyl ion. The value of p for the solvolysis of the 3-aryl derivatives was -1.5, suggesting some charge transfer to the 3-position. The 3-chlorocyclobutyl tosylates react to give only the inverted 3-chlorocyclobutyl acetates. The 3-ethoxy derivatives give -1: 1 mixtures of the corresponding acetates. Further information concerning these reactions was obtained via a b initio M O calculations a t the MP2/6-31G* theoretical level. They showed that except for the silyl substituents, all of the other 3-substituents led to a decrease in energy on rearrangement to the corresponding cyclopropylcarbinyl ion. The latter was found to have considerable homoallyl cation character when substituted at the 2-position. All of the results are in accord with the hypothesis that the rate-determining step with X = alkyl or aryl is the formation of a. bridged cyclobutyl cation that is a transition state for a stereospecific rearrangement to the corresponding cyclopropylcarbinyl ion. The reaction products are then formed from the latter ion.