The synthesis and characterization of nadimidized aromatic bisaspartimides and their polymerization to high-temperature-resistant laminating resins

4,4′-Bis(N²)-{4-[4-(2,3-bicyclo-[2.2.1]hept-5-ene-dicarboximido)phenoxy]-phenyl(-aspartimido)-di-phenyl ether (2NAD/1020) and various similar polymer percursors were synthesized from bismaleimides by the Michael addition of two moles of aromatic diamine followed by end capping of the resultant amino-terminated bisaspartimide groups with nadic anhydride. These precursors were characterized by using Fourier-transform infrared (FT-IR), proton, and carbon-13 nuclear magnetic resonance spectroscopies (¹H- and ¹³C-NMR). Thermal polymerization of 2NAD/1020 by heating it above its melting point gave a reddish brown thermoset polymer. The curing behavior and thermal stability of these nadimides were evaluated by differential scanning calorimetry and thermogravimetric analysis studies. Graphite fiber laminates were prepared from these polymer precursors and their mechanical properties evaluated. Gas Chromatography/Mass Spectra of the precursors and thermosets have given an understanding of their decomposition behavior. The structures of the thermosets were examined by FT-IR spectroscopy.     

Picosecond Time Resolved Studies of Photosensitized Electron Injection in Colloidal Semiconductors

Using a single picosecond pulse from a frequency-doubled Nd:YAG-mode-locked laser for excitation, we measured directly the rate of electron injection from the excited singlet state of eosin in the conduction band of colloidal TiO₂ particles. The rate constant for interfacial electron transfer is 9.5 × 10⁸s^?1 at 25°C and pH 3.     

Thermally polymerizable bisaryloxy-bisimido-bisphthalonitriles containing dimethylsilane,hexafluoroisopropylidene, ether,and keto groups: Synthesis,characterization, and NMR study

A proton-NMR study of the condensation reaction (step 1) of 4-(3′-aminophenoxy)phthalonitrile (4-3′APPN) ( I ) in an aprotic solvent with various aromatic dianhydrides demonstrated the formation of the corresponding bisamic acid within 5–10 min. There was no effect of the electron affinity of the used aromatic dianhydrides on the time of the condensation reaction and also no charge-transfer complex formation was indicated. Proton-NMR study of the synthesized bisaryloxy-bisimido-bisphthalonitriles at 250.1 MHz has revealed general findings for their NMR characterization. The coupling constant (J) value for the ortho-coupled protons of the phthalonitrile ring of the 4–3′-APPN portion is 8.8 ± 0.05 Hz and that for the ortho-coupled protons of the aminophenoxy ring of 4–3′-APPN is 8.1 ± 0.05 Hz. The coupling constant (J) values for ortho-coupled protons of the dianhydride portion range from 8.1 to 7.5 Hz. Various thermally polymerizable bisaryloxybisimido-bisphthalonitriles (BBBP) ( X, XI, XII , and XIII ) containing dimethylsilane, hexafluoroisopropylidene, ether, and keto groups, suitable for the development of thermooxidative stable, void-free composites, were synthesized by two methods. In method 1,4–3′-APPN ( I ) in N,N-dimethylacetamide (DMAC) was condensed (step 1) with bis(3,4-dicarboxyphenyl)dimethylsilane dianhydride (SIDA) ( II ), 4, 4′-hexafluoroisopropylidenediphthalic anhydride (6FDA) ( III ), bis(3,4-dicarboxyphenyl)ether dianhydride (ODPA) ( IV ), and 3,4,3′,4′-benzophenonetetracarboxylic dianhydride (BTDA) ( V ), respectively, to give the corresponding bisamic acids. Thermal cyclodehydration of the intermediate bisamic acid at 160°C gave the bisphthalonitriles. In method 2, the second step of thermal cyclodehydration was performed in situ in refluxing toluene. The characterization of the synthesized bisaryloxy-bisimido-bisphthalonitriles (BBBP) was performed using FT-IR, ¹H-NMR, ¹³C-NMR, mass spectroscopy, and elemental analysis. A preliminary study indicated that thermal-polymerization of these bisphthalonitriles (BBBP) gave tough, thermosetting polymers, useful for high-temperature applications. © 1993 John Wiley & Sons, Inc.     

Condensation polymerization of pyromellitic dianhydride with aromatic diamine in aprotic solvent: A reaction mechanism

Based on nuclear magnetic resonance (NMR) studies, a probable reaction mechanism was proposed for the condensation polymerization of pyromellitic dianhydride with aromatic diamines in aprotic solvent, N,N-dimethylacetamide (DMAc), to yield aromatic polyimides. The mechanism shows the essential role played by the solvent during polymerization reaction and in imidization. It explains the formation of polyamic acid and that of its high molecular weight buildup under the conditions in which solid dianhydride was added to the solution of diamine in DMAc. A prepolymer complex formation was observed, along with the main polyamic acid, when solid diamine was added to the solution of dianhydride in DMAc. The structure of the prepolymer was derived on the basis of NMR and its formation explained in the mechanism. The nature of the prepolymer was such that on treatment with anhydride it goes to polyamic acid.     

Synthesis, characterisation and mass spectrometric fragmentation of O-(chlorodifluoroacylated) alcohols

An indirect and uncatalysed esterification of chlorodifluoroacetic acid with polyfluoro and hydrocarbon alcohols has been developed. The method which involves the reaction between sodium chlorodifluoroacetate and alcohols in dimethylformamide (DMF) is particularly facile with polyfluorinated alcohols resulting in esters in 71-85% yield. The esters have been characterised on the basis of ¹H and ¹⁹F NMR and mass spectral data. The electron impact (EI) mass spectrometric fragmentation of these polyfluorinated esters have shown some interesting features which have been substantiated by using tandem mass spectrometry.     

Mass spectral studies on synthetic analogs of organophosphorus toxin occurring in dinoflagellate algae

A series of organophosphorus compounds related to PB-1 toxin [O,O-diphenyl N- cyclooctylphosphoramidate] occurring in dinoflagellate algae as fish toxin have been synthesized and subjected to mass spectral studies under electron ionization. The fragmentation pattern obtained for the compounds has been substantiated by performing tandem mass spectrometry experiments in product ion scan mode.     

Role of coordinated metal ions on the orientation of phthalocyanine based coatings

In the present work, we have investigated the molecular orientation of phthalocyanine films deposited on polycrystalline gold. Three films built from the following molecules are investigated: phthalocyanine (H(2)Pc), cobalt phthalocyanine (CoPc) and copper phthalocyanine (CuPc). The films are prepared by spin coating and drop casting methods. Orientation analysis has been performed using polarization dependent Fourier transform infrared (FTIR) spectroscopy using transmission and grazing angle reflectance mode. The FTIR study suggests that each phthalocyanine film contains both alpha- and beta-phases. H(2)Pc based films demonstrate deposition method dependence on the molecular orientation, while the CuPc and CoPc films preserve their molecular orientation independent of deposition method. Grazing angle analysis also suggests that CoPc films show negligible preferred orientation irrespective of film deposition methods. In literature, the band at 878cm(-1) in CuPc has been assigned to out-of-plane bending of C-H. Our grazing angle experiments suggest that this band cannot be assigned to out-of-plane bending vibrations of C-H. Accurate band assignments are also described here for the phthalocyanine system.     

Determination of Polycyclic Aromatic Hydrocarbons in Biodiesel Exhaust from Jatropha curcas and Chlorella variabilis by Gas Chromatography with Flame Ionization Detection

Biodiesel serves as a promising alternative to the conventional petroleum fuels and is considered to be a renewable source of energy which can be used in compression-ignition engines with minimum or no modifications. Two biodiesels derived from Jatropha curcas seeds and marine microalga Chlorella variabilis were substituted for petrodiesel and 16 priority polycyclic aromatic hydrocarbons (United States Environmental Protection Agency) were targeted for quantification through gas chromatography equipped with a flame ionization detector. For comparison, petrodiesel was selected as a control, and the analyte concentrations were calculated through calibration curves with correlation coefficient ranging from 0.9909 to 0.9999. The analytical figures of merit were determined for each analyte. The relative standard deviations for intra-day repeatability and inter-day reproducibility were in the range of 4.47–8.75%. The results indicated a significant decrease of around 77 and 68% in the overall polycyclic aromatic hydrocarbon concentrations in the particulate matter originating from J. curcas and microalga C. variabilis biodiesel, respectively. This study is perceived as an important step toward describing the green emission behavior of these biodiesels and their merits compared to the conventional petroleum-based fuels.     

Application of high performance liquid chromatography coupled to on-line solid-phase extraction-nuclear magnetic resonance spectroscopy for the analysis of degradation products of V-class nerve agents and nitrogen mustard

The detection and identification of the degradation products of nitrogen mustard and nerve agent VX by high performance liquid chromatography coupled to on-line solid-phase extraction-nuclear magnetic resonance spectroscopy (HPLC-UV-SPE-NMR) were demonstrated. The analytes selected for the study were N,N-dimethylaminoethanol (DMAE), N,N-diethylaminoethanol (DEAE), N,N-diisopropylaminoethanol (DIAE) and triethanolamine (TEA). Offline solid-phase extraction (SPE) followed by derivatization was applied to eliminate the interferents and make the analytes amenable for UV detection. Thereafter, chromatographically separated derivatives were trapped on on-line SPE cartridges. They were subsequently eluted and ¹H NMR and COSY spectra were obtained. The overall detection limits of the LC-UV-SPE-NMR method for the mentioned analytes were found to be 18, 23, 25, and 32 mg/L respectively. Applicability of the method to real samples was demonstrated by the analysis of samples provided during the 22nd OPCW official proficiency test. The method gave reproducible NMR spectra devoid of intense background signals.     

Higher order B-spline differential quadrature rule to approximate generalized Rosenau-RLW equation

In this article, B-spline-based collocation method is employed to approximate the usual and modified Rosenau-RLW nonlinear equations. The weighted extended B-spline (WEB-spline) is used as the modified form of B-spline as the usual B-splines fail to obey the Dirichlet boundary conditions. The WEB method is more general method that allows to discretize the domain into finite number of elements not necessarily start from the boundary points of the domain. Our method omits the linearization process of the nonlinear partial differential equation (PDE). Different cases are discussed by setting the parameter p=2,3,4, and 6 that appears in Rosenau-RLW equations. The error estimation is calculated, which gives good agreement of the exact solution.