Easily Processable Thermosets with Outstanding Performance via Smart Twisted Small-Molecule Benzoxazines.

High-performance aromatic polymers have excellent thermal, mechanical, and electrical properties and are lightweight, but it is highly challenging to deliver outstanding performances while still maintaining good processability of the precursors. Here, a new family of small-molecule benzoxazine resins with ortho-maleimide functionality is reported, which strikes an exceptional balance between the processability and performance. The excellent processability is attributed to the twisted molecular configurations of ortho-maleimide-substituted benzoxazines, which prevent intermolecular packing in the resin systems. The new benzoxazines can polymerize through multiple routes, which eliminate the twisted structures and create highly cross-linked polymer networks. The resulting new polymers are found to possess fascinating properties such as a high thermal stability (no Tg can be detected before 400 °C), excellent flame retardancy (a heat release capacity of 42.5 J g-1 K-1 ), and low dielectric constants (2.62-2.30 in the frequency range of 1 Hz to 10 MHz). The combined processability and versatility highlight the potential of smart benzoxazines in the preparation of high-performance thermosets, with important new applications that may span aerospace, transportation, and electronic packaging materials.

Effects of End-Caps on the Atropisomerization, Polymerization, and the Thermal Properties of ortho-Imide Functional Benzoxazines.

A new type of atropisomerism has recently been discovered in 1,3-benzoxazines, where the intramolecular repulsion between negatively charged oxygen atoms on the imide and the oxazine ring hinders the rotation about the C⁻N bond. The imide group offers a high degree of flexibility for functionalization, allowing a variety of functional groups to be attached, and producing different types of end-caps. In this work, the effects of end-caps on the atropisomerism, thermally activated polymerization of ortho-imide functional benzoxazines, and the associated properties of polybenzoxazines have been systematically investigated. Several end-caps, with different electronic characteristics and rigidities, were designed. ¹H and 13C nuclear magnetic resonance (NMR) spectroscopy and density functional theory (DFT) calculations were employed to obtain structural information, and differential scanning calorimetry (DSC) and in situ Fourier transform infrared (FT-IR) spectroscopy were also performed to study the thermally activated polymerization process of benzoxazine monomers. We demonstrated that the atropisomerization can be switched on/off by the manipulation of the steric structure of the end-caps, and polymerization behaviors can be well-controlled by the electronic properties of the end-caps. Moreover, a trade-off effect were found between the thermal properties and the rigidity of the end-caps in polybenzoxazines.

CF3+ and CF2H+: new reagents for n-alkane determination in chemical ionisation reaction mass spectrometry.

Alkanes provide a particular analytical challenge to commonly used chemical ionisation methods such as proton-transfer from water owing to their basicity. It is demonstrated that the fluorocarbon ions CF3+ and CF2H+, generated from CF4, as reagents provide an effective means of detecting light n-alkanes in the range C2-C6 using direct chemical ionisation mass spectrometry. The present work assesses the applicability of the reagents in Chemical Ionisation Mass Spectrometric (CI-TOF-MS) environments with factors such as high moisture content, operating pressures of 1-10 Torr, accelerating electric fields (E/N) and long-lived intermediate complex formation. Of the commonly used chemical ionisation reagents, H3O+ and NO+ only react with hexane and higher while O2+ reacts with all the target samples, but creates significant fragmentation. By contrast, CF3+ and CF2H+ acting together were found to produce little or no fragmentation. In dry conditions with E/N = 100 Td or higher the relative intensity of CF2H+ to CF3+ was mostly less than 1% but always less than 3%, making CF3+ the main reagent ion. Using O2+ in a parallel series of experiments, a substantially greater degree of fragmentation was observed. The detection sensitivities of the alkanes with CF3+ and CF2H+, while relatively low, were found to be better than those observed with O2+. Experiments using alkane mixtures in the ppm range have shown the ionisation technique based on CF3+ and CF2H+ to be particularly useful for measurements of alkane/air mixtures found in polluted environments. As a demonstration of the technique's effectiveness in complex mixtures, the detection of n-alkanes in a smoker's breath is demonstrated.

The pure rotational spectra of the open-shell diatomic molecules PbI and SnI.

Pure rotational spectra of the ground electronic states of lead monoiodide and tin monoiodide have been measured using a chirped pulsed Fourier transform microwave spectrometer over the 7-18.5 GHz region for the first time. Each of PbI and SnI has a X (2)Π1/2 ground electronic state and may have a hyperfine structure that aids the determination of the electron electric dipole moment. For each species, pure rotational transitions of a number of different isotopologues and their excited vibrational states have been assigned and fitted. A multi-isotopologue Dunham-type analysis was carried out on both species producing values for Y01, Y02, Y11, and Y21, along with Λ-doubling constants, magnetic hyperfine constants and nuclear quadrupole coupling constants. The Born-Oppenheimer breakdown parameters for Pb have been evaluated and the parameter rationalized in terms of finite nuclear field effects. Analysis of the bond lengths and hyperfine interaction indicates that the bonding in both PbI and SnI is ionic in nature. Equilibrium bond lengths have been evaluated for both species.

IR Band profiling of dichlorodifluoromethane in the greenhouse window: high-resolution FTIR spectroscopy of ν2 and ν8.

The IR spectrum of dichlorodifluoromethane (i.e., R12 or Freon-12) is central to its role as a major greenhouse contributor. In this study, high-resolution (0.000 96 cm(-1)) Fourier transform infrared spectra have been measured for R12 samples either cooled to around 150 K or at ambient temperature using facilities on the infrared beamline of the Australian Synchrotron. Over 14,000 lines of C(35)Cl2F2 and C(35)Cl(37)ClF2 were assigned to the b-type ν2 band centered around 668 cm(-1). For the c-type ν8 band at 1161 cm(-1), over 10,000 lines were assigned to the two isotopologues. Rovibrational fits resulted in upper state constants for all these band systems. Localized avoided crossings in the ν8 system of C(35)Cl2F2, resulting from both a direct b-axis Coriolis interaction with ν3 + ν4 + ν7 and an indirect interaction with ν3 + ν4 + ν9, were treated. An improved set of ground state constants for C(35)Cl(37)ClF2 was obtained by a combined fit of IR ground state combination differences and previously published millimeter wave lines. Together these new sets of constants allow for accurate prediction of these bands and direct comparison with satellite data to enable accurate quantification.

Geometries and bond energies of the He-MX, Ne-MX, and Ar-MX (M = Cu, Ag, Au; X = F, Cl) complexes.

Calculations on the He...MX, Ne...MX, and Ar...MX (M = Cu, Ag, Au; X = F, Cl) complexes at the CCSD and CCSD(T) levels of theory have been carried out. The geometries of the Ar-MF complexes are in good agreement to those determined via microwave spectroscopy. The RG...MX (RG = He, Ne, and Ar) dissociation energies for these complexes have been evaluated by extrapolation to the complete basis set limit. The importance of the inclusion of diffuse functions to the determined dissociation energies of these complexes are discussed with comparison to recent work. For the He...CuF and He...AuF complexes, the dissociation energies have been found to be significant, at approximately 26 kJ mol(-1), while the bonding in the chlorine analogues is only approximately 15 kJ mol(-1). The bonding between the helium and the metal atoms in the He...CuF and He...AuF complexes has been investigated by using an atoms-in-molecules (AIM) analysis together with an evaluation of the dipole/induced-dipole and ion/induced-dipole interactions. This analysis has shown that the bonding in these complexes is slightly covalent in nature. For the He...AgF and Ne...MF (M = Cu, Ag, Au) complexes the dissociation energy is much smaller and the AIM analysis shows the bonding is more electrostatic in nature. Calculations have also been carried out on He...AgCl and Ne...MCl (M = Cu, Ag, Au) complexes for the first time in addition to the Ar...MX (M = Cu, Ag, Au; X = F, Cl) complexes. The RG...MCl complexes are found to be more weakly bound than the corresponding RG...MF complexes as a result of the difference in electronegativity of the halogen. For each complex, bond lengths, rotational constants, and harmonic vibrational frequencies have also been evaluated.

Spectroscopic investigation of the A (1)A(")-X (1)A(') electronic transition of HSiNCO.

The first spectroscopic observation of the previously unknown species HSiNCO has been reported. HSiNCO was generated by the fragmentation of trimethylsilylisocyanate with a high-voltage discharge source. The 0(0)(0) band of the A (1)A(")-X (1)A(') transition has been recorded with full rotational resolution using laser-induced fluorescence spectroscopy and ground and excited state rotational and centrifugal distortion constants determined. Ten additional vibrational bands belonging to HSiNCO have also been observed in the laser-induced fluorescence spectrum and have been assigned based on predicted anharmonic vibrational frequencies. Due to the large change in geometry upon excitation, a number of axis-rotation peaks have been observed in the 0(0)(0) band and the axis-rotation angle (theta(T)) has been estimated to be 0.6 degrees +/-0.2 degrees. Dispersed fluorescence spectroscopy has been carried out and nu(8) (the N-C-O out-of-plane bending mode) and a number of overtones of nu(4) (the Si-H wagging mode) have been observed in the ground electronic state.

Spectroscopic investigation of the electronic A1A''-X1A' transition of HSiNC.

The first spectroscopic investigation of the A1A''-X1A' transition of HSiNC has been reported. The 0(0)(0) band of the A1A''-X1A' transition has been rotational resolved using laser-induced fluorescence spectroscopy, and ground- and excited-state rotational and centrifugal distortion constants were evaluated. Ten additional vibrational bands belonging to HSiNC have also been observed in the laser-induced fluorescence spectrum and have been assigned based on predicted anharmonic vibrational frequencies. Because of the large change in geometry upon excitation, a number of axis-rotation peaks have been observed in the 0(0)(0) band, and the axis-rotation angle (thetaT) has been estimated to be 1.0 +/- 0.2 degrees. Dispersed fluorescence spectroscopy has also been carried out, and a number of overtones of the nu3 fundamental (Si-H wagging mode) have been observed in the ground state, and its anharmonic parameter (x(e)) was evaluated.

Computational study on the structures of the [H, Si, N, C, O] isomers: possible species of interstellar interest.

Ab initio methods have been used to study the lowest lying [H, Si, N, C, O] isomers, which are of astrochemical interest. Over 20 [H, Si, N, C, O] isomers in the 1A' electronic state have been investigated at the MP2/aug-cc-pVTZ level of theory. Of these, the seven lowest isomers have been further investigated using different levels of theory, including B3LYP and QCISD(T). It has been found that the relative energies of the isomers in their ground electronic state (1A') are very dependent on the level of theory used with either the cis-HOSiCN or cis-HOSiNC isomers being the lowest in energy. Overall, the four lowest isomers are within 6 kcal/mol of each other, and a further three isomers are less than 15 kcal/mol higher in energy than the lowest lying isomer, including HSiNCO, which has recently been detected spectroscopically. Natural bond analysis has been carried out on the ground electronic states of the seven lowest lying isomers to examine their electronic structure. The enthalpies of formation of the seven lowest isomers have also been evaluated using the G3MP2 and G3B3 multilevel methods and show that the isomers are relatively thermodynamically stable. The structures and energies of lowest lying 1A'' and 3A'' electronic states of these isomers have also been investigated and show that for most of the isomers the optimized structures in these excited electronic states correspond to a transition state structure.

A three-dimensional multivariate image processing technique for the analysis of FTIR spectroscopic images of multiple tissue sections.

BACKGROUND: Three-dimensional (3D) multivariate Fourier Transform Infrared (FTIR) image maps of tissue sections are presented. A villoglandular adenocarcinoma from a cervical biopsy with a number of interesting anatomical features was used as a model system to demonstrate the efficacy of the technique. METHODS: Four FTIR images recorded using a focal plane array detector of adjacent tissue sections were stitched together using a MATLAB routine and placed in a single data matrix for multivariate analysis using Cytospec. Unsupervised Hierarchical Cluster Analysis (UHCA) was performed simultaneously on all 4 sections and 4 clusters plotted. The four UHCA maps were then stacked together and interpolated with a box function using SCIRun software. RESULTS: The resultant 3D-images can be rotated in three-dimensions, sliced and made semi-transparent to view the internal structure of the tissue block. A number of anatomical and histopathological features including connective tissue, red blood cells, inflammatory exudate and glandular cells could be identified in the cluster maps and correlated with Hematoxylin & Eosin stained sections. The mean extracted spectra from individual clusters provide macromolecular information on tissue components. CONCLUSION: 3D-multivariate imaging provides a new avenue to study the shape and penetration of important anatomical and histopathological features based on the underlying macromolecular chemistry and therefore has clear potential in biology and medicine.

Infrared spectroscopy of Li(NH3)n clusters for n=4-7.

Infrared spectra of Li(NH3)(n) clusters as a function of size are reported for the first time. Spectra have been recorded in the N-H stretching region for n=4-->7 using a mass-selective photodissociation technique. For the n=4 cluster, three distinct IR absorption bands are seen over a relatively narrow region, whereas the larger clusters yield additional features at higher frequencies. Ab initio calculations have been carried out in support of these experiments for the specific cases of n=4 and 5 for various isomers of these clusters. The bands observed in the spectrum for Li(NH3)(4) can all be attributed to N-H stretching vibrations from solvent molecules in the first solvation shell. The appearance of higher frequency N-H stretching bands for n > or =5 is assigned to the presence of ammonia molecules located in a second solvent shell. These data provide strong support for previous suggestions, based on gas phase photoionization measurements, that the first solvation shell for Li(NH3)(n) is complete at n=4. They are also consistent with neutron diffraction studies of concentrated lithium/liquid ammonia solutions, where Li(NH3)(4) is found to be the basic structural motif.

Microwave Spectrum, Structure, and Hyperfine Constants of Kr-AgCl: Formation of a Weak Kr-Ag Covalent Bond.

The pure rotational spectrum of the complex Kr-AgCl has been measured between 8-15 GHz using a cavity pulsed-jet Fourier transform microwave spectrometer. The complex was found to be linear and relatively rigid, with a Kr-Ag bond length of approximately 2.641 Å. The Kr-Ag stretching frequency was estimated to be 117 cm(-1). Ab initio calculations performed at the MP2 level of theory gave the geometry, vibration frequencies, Kr-Ag bond dissociation energy, and orbital populations. The Kr-Ag bond dissociation energy was estimated to be approximately 28 kJ mol(-1). The Kr-Ag force constant and dissociation energy are greater than those of Ar-Ag in Ar-AgCl. The chlorine nuclear quadrupole coupling constants show slight changes on complex formation. Ab initio orbital population analysis shows a small shift in sigma-electron density from Kr to Ag on complex formation. The combined experimental and ab initio results are consistent with the presence of a weak Kr-Ag covalent bond. Copyright 2001 Academic Press.