Vasile Cozan

Side chain thermotropic liquid crystalline polysulfone obtained from polysulfone udel by chemical modification

Abstract Polysulfone udel was chemically functionalized with chloromethylene functional groups via the chloromethylation reaction. A new azomethine dimesogen containing one phenolic hydroxyl functional group was recently synthesized and proved to exhibit a large nematic mesophase range in the liquid state. Further reaction of the dimesogen with the functionalized polysulfone using a transquaternization reaction led to new polysulfones bearing pendant rigid dimesogenic units––no spacer being involved in the chemical design of the polymer. The polymers were characterized by IR, 1H NMR spectroscopy techniques, and their thermotropic liquid crystallinity behaviour was studied by optical polarizing microscopy (PLM) and DSC measurements. Enantiotropic nematic mesophases were observed under the PLM. A dependence of the melting temperature on the degree of substitution was noticed.

Azomethine sulfone macromers with thermotropic liquid crystalline behavior

Abstract New azomethine sulfone macromers containing benzylideneaniline mesogens were prepared by the conventional methods available in the literature by condensing the sulfone aldehyde monomer with aromatic diamines (DA1–DA5) using N,N-dimethylformamide as solvent. The macromers (M1–M5) were confirmed by IR, 1H-NMR, and elemental analyses, and were characterized by thermogravimetric analysis and X-ray diffraction. Their thermotropic liquid crystalline behavior was studied using polarization light microscopy, thermo-optical analysis, and differential scanning calorimetry. A nematic texture was observed for macromers M1–M3 containing the two benzylideneaniline mesogens either connected by etheric (M1), methylenic links (M2), or directly coupled (M3). Conformational energy and mesogenic index (MI) calculations were performed and used to explain the TLC behavior of the macromers studied.

Polyazomethine with m-tolylazo side groups: thermal, dielectric and conductive behaviour

Using solution polycondensation, a new polyazomethine with m-tolylazo side groups (PAz) exhibiting thermotropic liquid crystalline phase was synthesised and its chemical structure was characterised with generally accepted methods. Its phase transition temperatures were detected with both polarising optical microscopy and differential scanning calorimetry. Using dielectric spectroscopy method, both real and imaginary parts of the permittivity were investigated in wide regions of temperature (from −100°C to 170°C) and frequency (from 1 Hz to 1 MHz). Analysis of frequency dependent permittivity allowed finding three relaxations (α, β1 and β2) in PAz. β-relaxations were described with the Arrhenius equation, whereas α-relaxation was described with the Vogel–Fulcher–Tammann equation. The alternating current conductivity (ACC) of PAz was studied in the same regions of temperature and frequency. The frequency dependent ACC was described with an exponent power equation. Presentation of ACC as a function of inverse temperature allowed us to describe ACC with the Arrhenius equation.

influence of chemical structure on processing and thermotropic properties of poly(siloxane-azomethine)s

A disiloxane dialdehyde was obtained from bis (chloromethyl)disiloxane and p-hydroxybenzal-dehyde and it was used in an equilibration (redistribution) reaction to synthesize an oligomeric dialdehyde. By solution polycondensation, starting from bis(formyl-p-phenoxymethyl)tetramethyldisiloxane and different organic diamines, poly(azomethine)s were obtained. In the case of aromatic diamines with high rigidity, which gave insoluble polymers, different approaches were tested in order to improve the solubility: the use of the dialdehyde having longer siloxane chain, or of a siloxane diamine in a copoly-condensation reaction. The polymers’ structures were confirmed by IR and 1H NMR spectroscopy and by elemental analysis. The structure-properties relationship was studied in terms of solubility, thermal and thermotropic behavior. Most of the obtained poly(azomethine)s has mesomorphic properties, which were studied by polarized optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray diffraction. The influence of aromatic diamines’ chemical structure on the processability of the siloxane-organic poly(azomethine)s was emphasized.

Kinetics of the nematic phase growth across the isotropic-nematic phase transition in polymer-dispersed liquid crystals

Polymer-dispersed liquid crystals (PDLCs) composed of poly(dimethyl siloxane), cured poly(dimethyl siloxane) and polysulfone (as matrices), and an azomethine compound (as an embedded mesogen varying in weight from 5 to 80%) were prepared via solvent-induced phase separation. After preparation, they were heated to the melt and then cooled; phase transitions upon both heating and cooling were detected with a differential scanning calorimeter and a polarising optical microscope (POM). The nematic droplets appearing in the POM images across the isotropic-nematic phase transition were treated statistically and described with principles of irreversible thermodynamics. Furthermore, kinetics of the nematic phase growth across this phase transition was studied and described analytically with the universal law for cluster growth. Both flexibility of the polymer matrix and the mesogen content in PDLCs were shown to influence the processes studied.

New siloxane–ester modified polysulfones by phase transfer catalysis

Chemical modification of a chloromethylated polysulfone was performed by using siloxane-containing aliphatic carboxylic salts as modification agents and phase transfer catalysis. The obtained substitution degrees ranged between around 0.1 and 0.9, as determined by 1 H NMR, IR and elemental analyses. The introduction of siloxane‐aliphatic moieties induced a decrease in the glass transition temperature (Tg) values of the obtained products in comparison to the starting polysulfone. All the modified polysulfones showed phase separation in optical microscopy. q 2000 Elsevier Science Ltd. All rights reserved.

Kinetics of the Isotropic‐Ordered Phase Transition in Binary Mixtures of Mesogenic Monomers and Polymers

Kinetics of the nematic phase growth in the melted liquid crystalline azomethine monomer, siloxane‐azomethine polymer, and their mixtures was studied under a deep cooling using polarizing optical microscopy. The nematic droplets revealed in the optical images across the phase transition were treated statistically and the resulting statistical size distributions were described using principles of irreversible thermodynamics. Analysis of the mean droplet diameter as a function of time allowed recognition of two regimes involved to the nematic phase evolution: (1) nucleation and rapid nucleus growth and (2) nucleus coarsening. Both regimes were quantitatively described with the universal law of the cluster growth.

Polyimides containing cycloaliphatic segments for low dielectric material

New polyimides have been synthesized by the reaction of 3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA) or/and 5-[2,5-(dioxotetrahydrofuryl)]-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride (DOCDA) with 4,4′-methylene dianiline (DDM). Polycondensation reactions were carried out in N, N-dimethylformamide solution and the resulting polyimides gave flexible free-standing films. The introduction of alicyclic moieties in the polyimide backbone improved the solubility of the resulting polymers and facilitated their processing while maintaining a high thermal stability. The dielectric constant values (measured at 106 Hz at room temperature), were found in the range of 3.14–2.83 and decreased with increasing of the alicyclic units content.

Synthesis and thermotropic properties of polyazomethines–containing side chain azobenzene moieties

Aromatic polyazomethines–containing azobenzene side groups have been synthesized by solution polycondensation reaction of aromatic dialdehydes bearing flexible spacers between the aromatic rings with aromatic diamines having preformed azobenzene side groups. Thermogravimetric analysis, differential scanning calorimetry, polarized optical microscopy, and wide angle X-ray diffraction have been used to evaluate their thermal and mesomorphic properties. The target polyazomethines showed nematic liquid crystalline phase, large mesophase range, and good thermal stability.

Pendant functional group copolyether sulfones. II. Modified copolyether sulfones with aminoazobenzene units

Modified copolyether sulfones with bulky azo pendant groups were synthesized by a polycondensation reaction of some polysulfones containing aldehyde groups with p-aminoazobenzene. The corresponding model compound and an azo oligomer were also prepared to compare their properties. The structure of the resulting compounds was confirmed by IR, 1H-NMR spectra, and elemental analyses. The polymers were characterized by reduced viscosity, thermogravimetric analysis, and differential scanning calorimetry. The photochemical behavior of the azoaromatic chromophores was followed by UV-visible absorption spectroscopy. Two kinds of photoreactions (photoisomerization and photodecoloration) operate in these polymers.