Elena Rusu

SOLVENT INFLUENCE ON THE ELECTRONIC ABSORPTION SPECTRA OF SOME AZOAROMATIC COMPOUNDS

Solvent-induced effects on the π–π* electronic absorption band frequencies of some azobenzene derivatives are described in terms of dipole–dielectric, solute–solvent, and hydrogen bonding interactions. A multiple linear regression equation for νmax was developed based on polarizability–polarity parameters and Kamlet–Taft solvatochromic parameters. Although the polarizability is a major contributor to the interactions in solutions, parameters related to the solvent polarity, hydrogen bond acidity, and hydrogen bond basicity are also statistically significant in determining the spectral shifts.

Anionic Nylon 6/Zinc Composite Materials: Evaluation of Thermal and Mechanical Behavior

This study deals with the experimentally investigated effect of zinc (Zn) particles on the thermal and mechanical properties of nylon 6/zinc composite materials. Nylon 6 and nylon 6 containing 6.0, 8.0, 12.0, 15.0, 20.0, and 25.0 wt.% of unmodified zinc particles, metal-polymer composite materials, were prepared by in situ anionic polymerization of є-caprolactam (CL) in the presence of metallic fillers using rotational molding technique. The characteristics, namely melting temperature, degree of crystallinity (first and second heating scan) and crystallization temperature, crystalline structure, thermal stability, and mechanical properties (flexural modulus, flexural strength, and notched Izod impact strength), of the nylon 6/zinc composites were determined for each sample. Different DSC, ATG, wide-angle X-ray diffraction, and mechanical measurements were performed. The results related to nylon 6 composites were compared with those obtained for pure nylon 6.

Nylon 6/TiO2 Composites by in situ Anionic Ring-Opening Polymerization of ϵ-Caprolactam: Synthesis, Characterization, and Properties

Two series of nylon 6/TiO2 composites were obtained via anionic ring opening polymerization of ϵ-caprolactam in the presence of untreated and surface-treated TiO2 with 3-aminopropyltriethoxysilane (APTEOS) as coupling agent by the rotational molding technique. The polymerization process was carried out using a system initiator/activator based on sodium dicaprolactamato-bis(2-methoxyethoxo)aluminate and N,N′-[methylene-di(4,4′-phenylene)bis-carbamoyl]bis-ϵ-caprolactam. All tests were performed at the initial polymerization temperature of 160° ± 2°C. The influence of both untreated and treated TiO2 particle concentration on the degree of conversion (DC), intrinsic viscosity [η], weight-average molecular weight , and water absorption of pure nylon 6 and its composite materials was investigated in the range of 0.0 to 8.0 wt.% TiO2. The thermal behavior and crystalline structures of pure nylon 6 and its composites have been studied in correlation with filler concentration by differential scanning calorimetry (DSC), thermogravimetry analysis (TGA), and room temperature wide-angle X-ray diffraction (WAXD). The mechanical characteristics, including tensile and flexural properties, elongation at break, and notched Izod impact strength, of nylon 6 and its composites as a function of TiO2 filler content were investigated for all samples. Experimental results revealed that the unmodified and surface-modified TiO2 as fillers had distinct influence on the degree of conversion, weight-average molecular weight, crystallization behavior, thermal stability, mechanical properties, and water absorption of nylon 6 matrix.

Evaluation of thermal and mechanical behavior of some anionic polyesteramide copolymers

A series of aliphatic polyesteramide copolymers were synthesized through by anionic ring opening copolymerization of є–caprolactam (CLA) with є–caprolactone (CLO) using the rotational molding technique. The thermal characteristics of the prepared polyesteramide copolymers have been studied by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and dynamic mechanical analysis (DMA). The tensile, flexural and impact strength tests were performed for copolymers characterization from point of view of mechanical properties. The DSC results showed that the presence of comonomer (CLO) affects the melting temperature (Tm), crystallization temperature (Tc) and degree of crystallinity (αDSC) (first and second heating scan) of the polyesteramide copolymers which decrease proportionally to the content of the CLO in the initial monomer feed. The data related to onset decomposition temperatures and Tpeak1 and Tpeak2 values indicates that the polyesteramide copolymers are more thermally stable than nylon 6 homopolymer. Also, dynamical mechanical analysis revealed that introduction of ester sequence into nylon 6 backbone decreased both the storage modulus and the glass transition temperature of resulted polyesteramide copolymers. The elongation at break and impact strength of the polyesteramide copolymers increase significantly with increasing initial CLO content while a decrease of their tensile and flexural properties occurs. The results related to polyesteramide copolymers were compared with those obtained for nylon 6 homopolymer.

About intermolecular interactions in binary and ternary solutions of some azo-benzene derivatives.

The nature and strength of the intermolecular interactions in the solutions of three azo-benzene derivatives (ADi, i=1, 2, 3) were established by solvatochromic effects in solvents with different electric permittivities, refractive indices and Kamlet-Taft constants. A quantum mechanical analysis corroborated with spectral data offered information about the excited state dipole moments and polarizabilities of the studied compounds. The separation of the supply of universal and specific interactions to the total spectral shift was made based on the regression coefficients from the equations describing the solvatochromic effect. Supplementary information about the composition of the first solvation shell and the energy in the solute-solvent molecular pairs were obtained analyzing the ternary solutions of ADi, i=1, 2, 3 compounds in solvent mixture Methanol (M)+n-Hexane (H).

New polysulfones with pendant groups of cinnamate type

Bisphenol A polysulfone with pendant chloromethyl groups in the ortho-ether position of the bisphenol A moieties was grafted with cinnamic structures by the nucleophilic chloro-displacement reaction with cinnamic acid and p-hydroxycinnamic acid, respectively. New functionalized polysulfones were characterized by different methods and have proven to be photosensitive.

Thin layers obtained by photolysis of 4,4′- diazidodiphenyl in solution †

It was observed that a solid layer precipitates on the fused silica window of the cell where 4,4′-diazidodiphenyl is irradiated in solution. The precipitate seems to be a branched and crosslinked polymer containing mainly azo, hydrazo and azepine units. The highest amount of azodiphenyl units was obtained in chloroform and the lowest in tetrahydrofuran. As a rule the layer surface was uneven, with scaly aspect. The layer seems to be composed of a thin continuous film on which adhered aggregates whose dimensions and density increase with radiation dose and content of azo units and decrease with solution temperature. The ratio of photocurrent to dark current was found to be in the range 2–30 if mercury discharge radiation of about 100 W/m2 irradiance was used.

1-[(E)-4-(Phenyl-diazen-yl)phen-yl]-3-pyrroline-2,5-dione.

The title compound, C16H11N3O2, displays a trans configuration with respect to the azo group. The molecule is non-planar; the maleimide ring forms a dihedral angle of 42.35 (4)° with the benzene ring bonded to its N atom and the mean plane of this benzene ring is rotated by 21.46 (8)° with respect to the azo group mean plane, which, in turn, forms a dihedral angle of 24.48 (7)° with the ‘terminal’ benzene ring. Molecules in the crystal are π–π stacked along the [100] direction with a mean interplanar distance of 3.857 (1) Å. In addition, C—H⋯O interactions link them into double layers parallel to the ac plane.

1,2-Bis(pyridin-4-yl)diazene–3,4,5-trihy­droxy­benzoic acid–methanol (3/2/2)

The title compound, 3C10H8N4·2C7H6O5·2CH4O, has a molecular crystal structure which results from the cocrystallization of gallic acid (GA), 4,4′-azodipyridine (AzPy) and methanol in a 2:3:2 molar ratio. The asymmetric unit comprises one molecule each of GA, AzPy and methanol in general positions and half a molecule of AzPy as this is located about a centre of inversion. In the crystal, all the components of the structure are associated via the extended system of hydrogen bonds (O—H⋯O and O—H⋯N) and π–π stacking interactions [centroid–centroid distance = 3.637 (3) Å] into two-dimensional supramolecular layers which are packed parallel to the [101] plane. The shortest perpendicular distance and the slippage between aromatic groups are 3.395 (3) and 2.152 (3) Å, respectively. The AzPy molecules display a trans conformation with respect to the azo groups.

Photoconductive films of conjugated polymers obtained by vacuum decomposition of aromatic diazides: Photopolycondensation of 4,4′-diazidodiphenyl

Abstract Films of poly(4,4′-trans-azodiphenyl) were obtained by vacuum photolysis of 4,4′-diazidodiphenyl. Transparent and smooth films of about 0.1 µm thickness and several nanometers average roughness were formed when the azide vapor flow was low enough relatively to the radiation intensity. These films absorb light at 405 nm and exhibit photoconductivity of 10–14Ω–1cm–1 under moderate illumination with incandescent lamps. When the azide vapor flow was too large, the films were uneven and opaque.