Mariana-Dana Damaceanu

SOLID‐STATE PROPERTIES OF MESOMORPHIC COPOLYMERS CONTAINING OXADIAZOLE AND FLUORENE UNITS

A series of copolymers containing oxadiazole and fluorene cromophores was synthesized by polycondensation of a diacid chloride incorporating one diphenylsilane linkage and a mixture of aromatic diamines containing oxadiazole and fluorene moieties. The solubility, thermal behavior, and photoluminescence ability of the thin polymer films were studied and compared with related heterocyclic polymers. These polymers are semicrystalline and form plastic mesophases in the first heating run, which brings about new ordered melted state processing opportunities. They exhibited blue photoluminescence in nanometric films, thus being promising candidates for manufacturing electroluminescent devices.

Six-member polyimides incorporating redox chromophores

This study focuses on the thermal, photo-optical and electrochemical characterization of some copoly(oxadiazole-naphthylimide)s containing tetramethyldisiloxane units. The thermal stability and glass transition temperatures of these copolymers were measured and compared with those of related polymers. The polymers were processed in very thin films having smooth surfaces, without pinholes or cracks. Upon irradiation with UV light the polymers showed photoluminescence maxima in the blue spectral range. Cyclic voltammetry was performed to obtain information about the electrochemical stability and reversibility of the redox processes of these polyimides. The HOMO and LUMO energy levels, and electrochemical and optical band gap values were calculated by using cyclic voltammetry and UV–Vis spectroscopy data, showing very good electron-injection and transport characteristics. These properties make the present polymers suitable for application in electroluminescent devices.

Dielectric Behavior of Thin Films made from poly(oxadiazole-naphthylimide)s

Oxadiazole-containing poly(naphthylimide)s were prepared by polycondensation reaction and their solid-state properties were investigated. Flexible films having good mechanical properties were made therefrom. The tougher polymer films were the subject of electrical insulating properties measurements. The dielectric constant values, measured at room temperature and in the frequency domain of 1 Hz–1 MHz, are in the range of 2.63–3.24, being lower or comparable with those of Kapton HN measured under the same conditions. The dielectric loss values are low, in the same range with those of Kapton HN. The dielectric spectroscopy data showed distinct subglass transitions for these polymers: γ relaxations with activation energies of 35 and 46 kJ/mol, and a β relaxation with the activation energy of 86 kJ/mol.

An easily functionalizable oligo(oxyethylene)- and ester-substituted poly(3,4-propylenedioxythiophene) derivative exhibiting alkali metal ion response

A new poly(3,4-propylenedioxythiophene) (PProDOT) derivative combining ion complexing oligoether units and a reactive ester group in the side chain obtained by oxidative chemical and electrochemical polymerization of the corresponding ProDOT monomer is described. The P(ProDOT-EO-ester) chemically synthesized after dedoping reveals a strong UV blue shift in THF in the presence of Na+ and K+, respectively, indicating conformational disordering and a substantially decreased conjugation of the polymer chain induced by ion complexation. Post-polymerization functionalization can be achieved by treatment with hydrazine hydrate leading to partial hydrazinolysis of the ester group. The electrogrowth process of the polymer on ITO is carried out using Bu4NClO4 or LiClO4 as supporting electrolyte, resulting in the formation of conductive thin films. Cyclic voltammetry reveals a slight shift of the redox peaks to lower potentials in the presence of Li+.

Study of thin films made from aromatic polymers containing six-member imide rings

This study was concerned with the synthesis and study of thin films made from polyimides containing naphthalene and oxadiazole rings. These polymers were prepared by polycondensation reaction in solution at high temperature of aromatic diamines containing preformed oxadiazole ring with a mixture 1: 1 of a naphthalene-containing dianhydride with hexafluoroisopropylidene-dianhydride. The resulting aromatic polymers containing six-member imide rings were soluble in polar amidic solvents and in less polar solvents, and their solutions gave flexible films having tough mechanical properties. The thermal stability and glass transition temperature of these polymers were measured and compared. The quality of the spin-coated films of these polyimides was investigated by atomic force microscopy. The photoluminescence properties of the polymers in solution and in thin films were studied to survey the color of emission. The UV absorption was also investigated to determine the Stokes shift and hence possible reabsorption effects, and the photo-optical stability of the polymers at high temperatures.

Copolyimides containing perylene and hexafluoroisopropylidene moieties

Three poly(ether-peryleneimide)s were prepared by one-step solution polycondensation reaction at high temperature of an aromatic diamine containing an oxadiazole ring and/or diphenylether units with a mixture of perylenetetracarboxylic dianhydride and hexafluoroisopropylidene-diphthalic dianhydride. The structure of the polymers was confirmed by Fourier transform-infrared analysis. These polymers possess good solubility in N-methylpyrrolidinone and can be processed into thin and tough flexible films. They are highly thermostable, up to 465°C, and display glass transition in the range of 227–266°C. The dielectric constant values of these polyimides at 25°C and in the frequency domain of 1 Hz to 100 kHz are in the range of 2.29–2.96. The photoluminescence spectra of those poly(ether-peryleneimide)s consist of the emission of perylenediimide chromophore and conjugated segments containing five-imide rings, without the emission from oxadiazole chromophore.

Dielectric and gas transport properties of highly fluorinated polyimides blends

The physicochemical properties of highly fluorinated polyimide blends were studied in order to highlight the advantages of employing a high content of fluorine atoms to tailor the properties of polyimide materials. Thus, dynamo-mechanical analysis was used to evidence the physical phenomena taking place during heating. The trend of storage modulus, loss modulus and loss factor tangent with temperature during and after the α relaxation was explored. The dielectric spectroscopy was carried out to investigate the dielectric behaviour at different temperatures and frequencies and to evaluate the values of dielectric constant, dielectric loss and electrical resistance. The dielectric spectroscopy data were corroborated with the dynamo-mechanical analysis to highlight the sub-glass transitions encountered in these blend films. Dielectric loss diagrams showed sub-glass transitions in the form of γ and β relaxations mainly due to the segmental mobility of the polymer chain components. The gas separation performance of some of the investigated blends was assesed, and their ability to achieve simultaneously higher gas permeability and higher selectivity was demonstrated.

Photo-optical and electrochemical behavior of novel heterocyclic copoly(naphthylimide-amide)s

This study is concerned with the synthesis and properties of new soluble quinoxaline-containing copoly(naphthylimide-amide)s having different flexible units such as ether, hexafluoroisopropylidene or diphenylsilane, in which the six-membered imide cycle is directly connected to the amide unit through a N-N bond. The polymers were successfully synthesized through the Yamazaki-Higashi polycondensation reaction of a mixture 1:1 of naphthalene-N,N’-bis(imido-amine) and 4,4′-{1,4-phenylene-bis[(3-phenyl-2,7-quinoxalinediyl)oxy]}dianiline or 4,4′-{oxy-bis[4,1-phenylene(3-phenyl-2,7-quinoxalinediyl)oxy]}dianiline with 4,4′-hexafluoroisopropylidene-bis(benzoic) acid, 4,4′-diphenylsilane-bis(benzoic) acid or with 4,4′-oxy-bis(benzoic) acid. These poly(imide-amide)s exhibited good solubility in common aprotic solvents, and the resulting polymer solutions were processed into amorphous thin films with homogeneous and neat surfaces. Their thermal characterization indicated a moderate to high thermal stability and no glass transition. The photoluminescence study of polymers both in solution and film state showed their ability for blue light color emission. The HOMO and LUMO energy levels were calculated by using cyclic voltammetry and UV–vis spectroscopy data, showing good electron injection and transport characteristics.

Copoly(1,3,4-oxadiazole-naphthylimide)s containing siloxane units in the main chain: synthesis and properties

This study was concerned with the synthesis and properties of new soluble copolyimides containing naphthalene, oxadiazole and tetramethyldisiloxane units. These copolyimides were prepared by two-step polycondensation reaction in solution of aromatic diamines containing preformed oxadiazole ring with a mixture 1 : 1 of naphthalene tetracarboxylic dianhydride and tetramethyldisiloxane- [1,3-bis(4′-phthalic anhydride)]. The structure of these polymers was confirmed by Fourier transform infrared and 1 H-NMR spectroscopy. The solubility, thermal stability and glass transition temperature of these copolyimides were measured and compared with those of related polyimides which do not contain siloxane groups. All these polymers emitted an intense blue color light upon irradiation with UV light. These copoly(oxadiazole-naphthylimide)s could be considered promising candidates for organo-soluble high-performance polymers for use in novel technological applications.

A new sensitizer containing dihexyloxy-substituted triphenylamine as donor and a binary conjugated spacer for dye-sensitized solar cells

The synthesis and application to dye-sensitized solar cells (DSSC) of a new dihexyloxy-substituted triphenylamine-based organic dye is reported. The dye design, based on the push–pull concept, consists of dihexyloxy-substituted triphenylamine as an electron donor and a cyanoacrylic acid as an anchoring group and electron acceptor connected through a π-conjugated bridge. The electron spacer containing furan and thiophene moieties was employed in the dye sensitizer for expansion of the π-conjugated fragment to adjust the absorption spectra and HOMO–LUMO levels of the dye. The relationship between the dye chemical structure and the photophysical, electrochemical, and photovoltaic properties determined by spectral, electrochemical, photovoltaic experiments, and density functional theory calculations was thoroughly investigated. The photovoltaic performance of the dye as sensitizer was assessed in DSSC cells realized using electrolytes containing the iodide/triiodide redox couple. The cells obtained with the new dye show a power conversion efficiency of 5.14%, without using any coadsorbant and optimization.