The diamides and disulfonamides m-C6H4(CONHAr)2 (Ar = Ph, 1; p-n-BuC6H4, 2, 2,4,6-Me3C6H2, 3), m-C6H4(SO2NHPh)2, 4, and 2,6-C6H3N(CONHPh)2, 5, readily synthesized on a multigram scale, bind strongly to halides and acetate in organic solvents with Ka's as high as 6.1 × 104 (NMR spectroscopy). The binding stoichiometry is 1:1 in solution for all cases except for the 4·F- and 4·OAc- complexes, where both 1:1 and 1:2 binding stoichiometries were found. The association constants in CD2Cl2 (1H NMR) follow the trend Cl- > Br- > I- for all the receptors. F- and OAc- binding may be stronger or weaker than Cl- depending on the nature of the receptor. The presence of the pyridine nitrogen in 5 and of the more rigid amide in 1−3 and 5 vs the less rigid sulfonamide structure in 4 increases selectivity for smaller anions. The enthalpy and entropy of formation for 2·Cl- were ΔH = −31 kJ/mol; ΔS = −23 J/(mol·K) (VT-NMR). The X-ray structure of [PPh4]2[1·Br][Br]·CH2Cl2, shows 1:1 complexation of Br- via two N−H···Br- hydr...

Hydrogen Bonding in Anion Recognition: A Family of Versatile, Nonpreorganized Neutral and Acyclic Receptors.

The heat and flame resistance of high performance fibres are reviewed according to the literature data. The performance is discussed considering the physical and chemical structure of the fibres. Some selected high performance fibres are then evaluated using the cone calorimeter as a fire model to provide realistic data on the fire behaviour of the fibres. They are also examined in terms of heat resistance using combined TGA/DSC. The results are discussed and compared with literature data. Heterocyclic rigid-rod polymers (poly (p-phenylene-2,6-benzobisoxazole or PBO (Zylon®) and poly(2,6-diimidazo (4,5-b:4′,5′-e) pyridinylene-1,4 (2,5-dihydroxy) phenylene or PIPD (M5)) exhibit the best performance (little or contribution to fire, low smoke and good heat resistance) and offer a good combination between heat and flame resistance and mechanical properties. Copyright © 2002 John Wiley & Sons, Ltd.

Heat resistance and flammability of high performance fibres: A review

A readily available non-preorganized neutral acyclic halide receptor with an unusual nonplanar binding conformation

Selected aromatic amides were used to model the chemical reactivity of aromatic polyamides found in thin-film composite reverse osmosis (RO) membranes. Chlorination and possible amide bond cleavage of aromatic amides upon exposure to aqueous chlorine, which can lead to membrane failure, were investigated. Correlations are made of the available chlorine concentration, pH, and exposure time with chemical changes in the model compounds. From the observed reactivity trends, insights are obtained into the mechanism of RO membrane performance loss upon chlorine exposure. Two chemical pathways for degradation are shown, one at constant pH and another that is pH-history dependent. An alternative strategy is presented for the design of chlorine-resistant RO membranes, and an initial performance study of RO membranes incorporating this strategy is reported. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1173–1184, 2003

Oxidative degradation of polyamide reverse osmosis membranes: Studies of molecular model compounds and selected membranes

In the present work, the thermal transformations of Nomex [poly(m-phenylene isophthalamide)] fibers have been investigated up to a temperature of 1173 K. The main stages of the pyrolytic degradation of the fibers were determined by thermal analysis, and their chemical and morphological evolution through the different steps was subsequently followed by Fourier transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM) measurements, respectively. The degradation starts with the cleaving of hydrogen bonds at approximately 633 K, which leads to a disordering of the polyaramide chains on the nanometer scale. The next decomposition step takes place between 673 and 873 K with the disruption of the amide bonds, the subsequent breaking of the polyaramide chains into smaller units, and their condensation into large polyaromatic compounds. From 873 K onward, the reaction progresses by the dehydrogenation of the polyaromatic structures and their arrangement into graphite-like assemblies, resulting in th...

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Atomic Force Microscopy and Infrared Spectroscopy Studies of the Thermal Degradation of Nomex Aramid Fibers

Thermal degradation behavior of poly(1,3-phenylene isophthalamide) and poly(chloro-2,4-phenylene isophthalamide) was investigated with the aid of some appropriate model compounds. The pyrolysis products of these materials were identified by gas chromatography (GC), gas chromatography/Fourier transform infrared spectroscopy (GC/FT-IR), and gas chromatography/mass spectrometry (GC/MS). The residual chars were characterized by IR spectroscopy. Thermogravimetric analysis (TGA) was applied to study the effect of end-group concentration on the degradation characteristics of the two polyamides. Kinetic parameters that describe the thermal degradation of the polyamides were also evaluated by TGA. The results of this investigation suggest that the thermal decomposition of these aromatic polyamides involves homolytic as well as hydrolytic cleavages of the amide units.

Aromatic polyamides. II. Thermal degradation of some aromatic polyamides and their model diamides

The synthesis of some wholly aromatic polyamides based on unsubstituted and chloro- and nitrosubstituted diamines by low temperature solution polymerization is described. Poly( 1,3-phenylene isophthalamide) and poly(chloro-2,4-phenylene isophthalamide) were selected for further investigation. To study the two polyamides on a systematic basis their model diamides were synthesized. These materials were characterized with respect to chemical structure and purity by elemental analysis, infrared (IR), and nuclear magnetic resonance (NMR) spectroscopic techniques. The usefulness of the model compounds in the interpretation of the polymer spectra is also demonstrated.

B. D. Forman

Papers

Aromatic polyamides. II. Thermal degradation of some aromatic polyamides and their model diamides

Aromatic polyamides. I. Synthesis and characterization of some aromatic polyamides and their model diamides