Mustapha Majdoub

Coupling focused microwaves and solvent-free phase transfer catalysis: Application to the synthesis of new furanic diethers

Abstract A new family of furanic ethers was obtained by alkylation of 2,5-furandimethanol or furfuryl alcohol under microwave in phase transfer catalysis (PTC) conditions in the absence of solvent. Products were synthesized in good yields (> 80 %) within 10 min or less. Compounds were analysed by NMR, mass spectrometry and their thermal behaviours were studied by DSC. When compared to conventional heating, everything equal elsewhere, reaction times were improved under microwave conditions at a restitute power of 30 Watts when performed under stirring in a monomode reactor (Synthewave 402 Prolabo).

New anthracene-based soluble polymers: optical and charge carrier transport properties

A series of anthracene-based polymers (P1–3) have been synthesized via the Wittig polycondensation. These organic materials were soluble in common organic solvents and show good film-forming abilities. Their macromolecular structures were characterized by NMR, FT-IR spectroscopies and steric exclusion chromatography, their thermal behaviors were analyzed by differential scanning calorimetry and their HOMO-LUMO energy levels were estimated by cyclic voltammetry. The optical properties of these π-conjugated systems were investigated by UV-visible absorption and photoluminescence spectroscopies. The effect of the spacer-group structure on the photo-physical behavior, π-π stacking ability and charge carrier transport properties of the polymer has been studied.

Electrical properties of ITO/benzylated cyclodextrins (β-CDs (Bz))/Al diode structures

Abstract Investigations of the electrical characteristics of benzylated cyclodextrins (β-CDs (Bz)) diodes are reported. We present current–voltage characteristics and impedance spectroscopy measurements performed on partially benzylated cyclodextrins β-CDs (Bz) thin films in sandwich structures ITO/b-CDs (Bz)/Al. The static electrical characterizations show a space charge limited conduction (SCLC) and a conductivity with power low frequency behavior characteristic of a hopping transport in disordered materials. The impedance spectra can be discussed in terms of an equivalent circuit model designed as a parallel resistor Rp and capacitor Cp network in series with resistor Rs. We extract numerical values of these parameters by fitting experimental data. Their evolution with bias voltages has shown that the SCLC mechanism is characterized by an exponential trap distribution. We estimated from the capacitance voltage characteristic an acceptor concentration of about 1011 cm−3 due to trap states.

Charge transfer processes in polymer light-emitting diodes

Optical characterisation of an organic soluble poly (paraphenylene vinylene) (PPV) derivative involving an alkyloxy pendant group on the phenylene ring has shown a shift of the absorption and emission towards longer wavelengths in comparison to PPV ones. The changes of the optical characteristics are ascribed to the redistribution of the π molecular orbital over the phenylene ring induced by the alkyloxy substituent. The comparison of the absorption and emission of the PPV derivative in solution or as a thin layer shows the role of the interchain interactions in condensed matter. Another example of the importance of charge transfer processes in PLED is provided by the indium tin oxide (ITO)/poly (vinyl carbazole) (PVK) hole transport layer interface. The weakening of the ITO absorption in the UV resulting from interband transitions has been interpreted by the depletion of the ITO free carriers at the contact of PVK. The shift towards longer wavelengths of the plasma frequency in the near infrared confirms the reduction of the free electron concentration in ITO, which has been estimated to 30% using the Drude free electron theory. The formation of a dipole layer at the interface can account for such charge transfers.

The effect of synthesis procedure on physical properties of poly(p-phenylene vinylene) derivatives

Abstract We have synthesized two poly( p -phenylene vinylene) (PPV) derivatives. The first one consists of a copolymer formed by a random succession of phenylene vinylene and ether groups and the second one is characterized by a pendant side chain containing ether groups hereafter referred to as polyXI and C8-PPV respectively. The polymer’s chemical structures were characterized by 13 C solid state NMR, FTIR and microanalysis. Thermal and structural properties were studied by differential scanning calorimetry and X-ray diffraction. The results were compared to pristine PPV. The effect of pendant side chain was discussed. Moreover, spectroscopic properties were investigated by means of photoluminescence and electron paramagnetic resonance and correlated to the material structure. From these studies we were able to present a possible explanation for the C8-PPV insolubility.

New Blue-Photoluminescent Semi-Conducting Polymer Derived from Fluorinated Bisphenol A

A new confined p-phenylenevinylene (PPV)-type polymer (BPAF-PPV ) has been synthesized using Wittig condensation. The chemical structure of the polymer was well defined by 1H-NMR, 13C-NMR, and FT-IR spectroscopic analysis. BPAF-PPV contains oligomeric PPV units separated by hexafluoroisopropylidene groups in the main chain; it is fully soluble in common organic solvents and has a number-average molecular weight of 4570 g mol-1. Differential scanning calorimetry indicates that BPAF-PPV is amorphous and displays a glass transition temperature of 114 °C. The optical properties of the polymer were investigated by UV-visible absorption and photoluminescence spectroscopies. Its thin film showed a blue photoluminescence with a narrow emission spectrum. A high photoluminescence quantum efficiency of about 83% was determined in dilute solution. From the cyclic voltammetry analysis, the electrochemical bandgap was estimated to be 3.08 eV. A single-layer diode device of the configuration indium-tin oxide/ BPAF-PPV/aluminium has been fabricated and has a relatively low turn-on voltage of 3.0 V.

Solid-State Polymerization of Poly(ethylene furanoate) Biobased Polyester, I: Effect of Catalyst Type on Molecular Weight Increase

In this work, we report the synthesis of poly(ethylene furanoate) (PEF), catalyzed by three different catalysts, namely, titanium (IV) isopropoxide (TIS), tetrabutyltitanate (TBT), and dibutyltin (IV) oxide (DBTO), via the two-stage melt polycondensation method. Solid-state polymerization (SSP) was conducted at different reaction times (1, 2, 3.5, and 5 h) and temperatures 190, 200, and 205 °C, under vacuum. The resultant polymers were analyzed according to their intrinsic viscosity (IV), end groups (–COOH), and thermal properties, via differential scanning calorimetry. DSC results showed that the post polymerization process was favorable to enhance the melting point of the prepared PEF samples. As was expected, the intrinsic viscosity and the average molecular weight of PEF increased with the SSP time and temperature, whereas the number of carboxyl end-groups was decreased. A simple kinetic model was also developed and used to predict the time evolution of polymers IV, as well as the carboxyl and hydroxyl content of PEF during the SSP. From both the experimental measurements and the theoretical simulation results it was proved that the presence of the TIS catalyst resulted in higher transesterification kinetic rate constants and higher reaction rates. The activation energies were not much affected by the presence of different catalysts. Finally, using DBTO as a catalyst, the polyesters produced have higher crystallinity, and as a consequence, higher number of inactive carboxyl and hydroxyl groups.

Synthesis, characterization and optical properties of distyrylanthracene-based polymers

Distyryl- and nitrodistyrylanthracene-based polymers (P1 and P2, respectively) have been synthesized and characterized. The polymers are fully soluble in common organic solvents and have number-average molecular weights of 18 570 and 23 480 g mol−1 for P1 and P2, respectively. The optical properties of the polymers were investigated by UV-visible absorption and photoluminescence spectroscopies. The optical gaps were estimated from the absorption-onsets of the polymer films; their values were 2.79, 2.75 eV for P1 and P2, respectively. A blue photoluminescence was observed in dilute solution. In solid thin film, Π–Π interactions influence the optical properties, and red-shifted photoluminescence spectra were obtained; a green emission (573 nm) for P1 and an orange one (605 nm) for P2 were observed. The HOMO and LUMO levels were estimated using cyclic voltammetry analysis. Single-layer devices of the indium-tin oxide/polymer/aluminum configuration were fabricated and showed relatively low turn-on voltages (5.14 V for P1 and 5.00 V for P2).

New Semiconducting Poly(arylene sulfide)s: Synthesis, Characterization, and Optical Properties

New semiconducting soluble poly(arylene sulfide)s were synthesized by Wittig polycondensation. The arylene moieties consist of distyrylbiphenyl (P1) and distyrylbithiophene (P2) π-conjugated systems. The polymers are fully amorphous and show good thermal stability. The absorption and photoluminescence properties of the polymers were investigated. P1 film has an optical gap of 2.95 eV and exhibits green-blue fluorescence. P2 shows a longer effective conjugation length with a gap of 2.42 eV and emits in the orange region. The HOMO/LUMO energy levels were estimated by cyclic voltammetry measurements. Single-layer diodes were fabricated and show relatively low turn-on voltages.

Optimized Synthesis According to One-Step Process of a Biobased Thermoplastic Polyacetal Derived from Isosorbide

This paper describes both the synthesis and characterization of a biobased and non-aromatic polyacetal produced from the reaction between isosorbide and methylene chloride. The reaction was conducted in an aprotic dipolar and harmless solvent using a one-step, fast and economical procedure. The chemical composition of this polymer was investigated using Nuclear Magnetic Resonance and Fourier Transform Infra-Red spectroscopies. The molecular weights were examined by size exclusion chromatography and MALDI-TOF spectrometry. The synthesis conditions (concentration, mixing speed, solvent nature, stoichiometry, addition mode of one reactan) were found to strongly influence both polymer architecture and reaction yield. Under moderated stirring conditions, the polyacetal was characterized by a larger amount of macro-cycles. Inversely, under higher intensity mixing and with an excess of methylene chloride, it was mainly composed of linear chains. In this latter case, the polymeric material presented an amorphous morphology with a glass transition temperature (Tg) close to 55 °C. Its degradation temperature was evaluated to be close to 215 °C using thermogravimetry according to multi-ramp methodology. The chemical approach and the physicochemical properties are valuable in comparison with that characteristic of other isosorbide-based polyacetals.