Polymerization of 2-hydroxyethyl methacrylate by hydro/solvothermal technique in presence of nanographene: electrical and thermal degradation characterization

Nanocomposites of poly(2-hydroxyethyl methacrylate) (PHEMA) loaded with 1.7 mass%, 6.5 mass% and 9.0 mass% nanographene were prepared by hydro/solvothermal technique. The main peaks of the nanographene and amorphous polymer structure were revealed by X-ray diffraction (XRD) analysis. Nanocomposites were characterized by SEM, DSC and TGA techniques. The dielectric constant (ε?), the dielectric loss factor (ε?), the loss tangent (tanδ) and the conductivity (σ_ac) were measured using a dielectric analyzer in a frequency range from 100 Hz to 2 kHz. Also, current (I)–voltage (V) measurements were carried out. It is well known that nanocomposite formation causes an improvement of many properties for a polymer, providing enhanced properties such as conductivity and thermal stability. This investigation was done to understand whether the presence of nanographene causes changes in the degradation pathway of poly(HEMA) prepared by hydro/solvothermal technique. For this aim, pure poly(HEMA) and nanocomposites were heated from room temperature to 500 °C. The characterization of degradation products for the cold ring fractions (CRFs) and trapped at???196 °C (in liquid nitrogen) was investigated by means of FT-IR, ¹H, ¹³C-NMR spectroscopic and GC–MS techniques. The FT-IR, NMR and GC–MS data showed that depolymerization corresponding to monomer (2-hydroxyethyl methacrylate) was the most important product trapped at CRF and???196 °C in the thermal degradation of nanocomposites. As the nanographene loading increased in composite systems, the rate of depolymerization of poly(HEMA) increased compared to pure poly(HEMA). The nanographene particles in the composite systems acted as a mass barrier that retards the escape of the volatile products

     

New conducting polymers, 3. Doping,stability, electrical,and optical characteristics of poly-(P-phenylphosphoethynediyl)

Studies on direct-current electrical conductivity and optical properties of a new solution of processable conducting polymer are reported. Electrical conductivity of thin films of the polymer on glass plate at room temperature was 6×10⁻⁶ S/cm. Study of conductivity with variation of temperature does not provide any definite thermal activation energy, which is in accordance with the amorphous nature of polymer. Optical absorption data adopting the Bardeen equation showed that maximum ‘optical gap’ (E _g ) is 3.30 eV. Doping with Br₂-vapor was found to be only partially effective in decreasingE _g by 0.43 eV. The polymer was found to be quite stable under normal atmospheric conditions. Environmental stability of both undoped and doped polymer has been discussed. Part 2: [5]     

Dimensionally and thermally stable polymer,containing disordered graphitic structure and adamantane

In an attempt to develop a low‐k interlayer dielectric, adamantane‐diphenyldiethynyl moiety containing oligomer is prepared. Oligomerization of 1,3,5,7‐tetrakis[3/4‐ethynylphenyl]adamantane ( 4 ) is accomplished by a Glaser–Hay oxidative coupling with 1,3,5‐triethynylbenzene and phenylacetylene end‐capping agent. The CHCl₃ soluble oligomer is then thermally treated by step‐curing at 200, 300, 380, and 450 °C for 30 min at each temperature under nitrogen flow to render a shiny void‐free black polymer. TGA analysis indicates that the polymer is stable under nitrogen up to 500 °C with a marginal decomposition up to 800 °C. Solid‐state ¹³C NMR, Raman scattering, and FTIR are used to characterize the structure of the polymer. The polymer consists of amorphous carbon networks with the adamantane moieties and nanosized graphitic regions (clusters), which are generated from the thermal crosslinking of the diphenyldiethynyl units. It shows a remarkably low linear coefficient of thermal expansion (～25 ppm/°C), presumably due to the presence of the disordered graphitic structure. Its high density (～1.21 g/cm³), refractive index (～1.80 at 632 nm), and Young's modulus (～17.0 GPa) are also consistent with the interpretation. This study reveals important details about the effect of microscopic structure on the macroscopic properties of the highly crosslinked polymer. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6909–6925, 2006     

Preparation and characterization of a nitrogen-doped mesoporous carbon aerogel and its polymer precursor

Nitrogen-containing carbon aerogel was prepared from resorcinol–melamine–formaldehyde (R–M–F) polymer gel precursor. The polymer gel was supercritically dried with CO₂, and the carbonization of the resulting polymer aerogel under nitrogen atmosphere at 900 °C yielded the carbon aerogel. The polymer and carbon aerogels were characterized with TG/DTA–MS, low-temperature nitrogen adsorption/desorption (??196 °C), FTIR, Raman, powder XRD and SEM–EDX techniques. The thermal decomposition of the polymer aerogel had two major steps. The first step was at 150 °C, where the unreacted monomers and the residual solvent were released, and the second one at 300 °C, where the species belonging to the polymer network decomposition could be detected. The pyrolytic conversion of the polymer aerogel was successful, as 0.89 at.% nitrogen was retained in the carbon matrix. The nitrogen-doped carbon aerogel was amorphous and possessed a hierarchical porous structure. It had a significant specific surface area (890 m² g^?1) and pore volume (4.7 cm³ g^?1). TG/DTA–MS measurement revealed that during storage in ambient conditions surface functional groups formed, which were released upon annealing.     

Synthesis and electrochemical characterization of aPEO-based polymer electrolytes

In this paper, the preparation and purification of an amorphous polymer network, poly[oxymethylene-oligo(oxyethylene)], designated as aPEO, are described. The flexible CH₂CH₂O segments in this host polymer combine appropriate mechanical properties, over a critical temperature range from −20 to 60 °C, with labile salt-host interactions. The intensity of these interactions is sufficient to permit solubilisation of the guest salt in the host polymer while permitting adequate mobility of ionic guest species. We also report the preparation and characterisation of a novel polymer electrolyte based on this host polymer with lithium tetrafluoroborate, LiBF₄, as guest salt. Electrolyte samples are thermally stable up to approximately 250 °C and completely amorphous above room temperature. The electrolyte composition determines the glass transition temperature of electrolytes and was found to vary between −50.8 and −62.4 °C. The electrolyte composition that supports the maximum room temperature conductivity of this electrolyte system is n = 5 (2.10 × 10⁻⁵ S cm⁻¹ at 25 °C). The electrochemical stability domain of the sample with n = 5 spans about 5 V measured against a Li/Li⁺ reference. This new electrolyte system represents a promising alternative to LiCF₃SO₃ and LiClO₄-doped PEO analogues.     

Dielectric spectroscopy of nanocomposites based on iPP and aPS treated in the water solutions of alkali metal salts

In this paper, a new simple and environmentally friendly treatment technique for obtaining polymer nanocomposites with appropriate dielectric properties has been presented. Sheets of isotactic polypropylene and atactic polystyrene were immersed in 3 saturated water solutions of alkali metal salts (LiCl, NaCl, and KCl) at 2 fixed temperatures (23°C and 90°C), and 3 DC electrical potentials (+4 kV, −4 kV, and ground potential) were applied. A quantification of alkali metals in the polymer sheets was conducted by inductively coupled plasma optic emission spectrometry. The obtained concentration values were from 7.38·10⁻⁹ mol/cm³ to 1.25·10⁻⁷ mol/cm³. The qualitative analysis of potassium distribution in the polymer matrix was conducted by time‐of‐flight secondary ion mass spectrometry cross‐sectional record. The relative dielectric constant (ε′) of samples was investigated in the frequency range from 20 Hz to 9 MHz at the constant temperature of 22°C. Stable values of ε′ in fully measured frequency range were observed for both pure and treated samples. Next, the results of the dielectric spectroscopy measurements were compared and established the kind of treatment that provided the highest value of ε′. The relationship between the concentrations of alkali metals and the values of relative dielectric constant was determined for the samples obtained by a treatment at 90°C and +4 kV.     

Growth and Thermal,Electrical, Structural Characterization of Mixed Hydrated Single Crystal

Mixed single crystal was made by mixing saturated aqueous solutions of NiSO₄ · 6H₂O and CuSO₄ · 5H₂O by volume (80:20) and the mixture was kept to form the crystals at room temperature by slow evaporation process. After some days, big pieces of greenish blue, dark colored crystals were grown. To determine the weight of NiSO₄ · 6H₂O and CuSO₄ · 5H₂O in the crystal, Ni-DMG complexiometrical and EDTA gravimetrical analysis was done respectively. From this analysis it was concluded that 5.8 molecules of water of crystallization is present in the mixed single crystal. The crystals were characterized by UV-Visible, FTIR and single crystal X-ray diffraction studies. From single crystal XRD lattice parameters have been calculated. All these structural analysis confirms formation of new single crystal. Further, DTA-TGA, dc electrical conductivity and dielectric constant studies were done from the room temperature to 400 °C.From DTA studies it was observed that 5.8 molecules of water of crystallization get dehydrated in four major steps at temperature 115 °C, 150 °C, 240 °C and 325 °C respectively corresponding to the detachment of 1 mole, 3 moles, 1 mole and 0.8 mole of water of crystallization. DC electrical conductivity and dielectric constant studies also show close agreement to the dehydration steps. The observed peaks in the conductivity verses temperature graph have been explained on the basis of release of water molecules and subsequent dissociation of these released water molecules into H⁺ and OH⁻ ions.     

ESR and electrical conduction in polypropiolamide

ESR and electrical conductivity measurements have been made on a recently prepared polymer, polypropiolamide. The polymer was obtained as a fine powder which exhibited a nearly Lorentzian line with a width between derivative maxima of 5.2 ± 0.1 gauss and a g value of 2.0036 ± 0.0005. The signal intensity increased with increasing molecular weight. The signal was retained in a dilute solution in formic acid with a slight narrowing of the line. Permanent changes were produced in the spectra at room temperature by heat treatments of the polymer at temperatures up to 800°K. The changes were similar for samples sealed in tubes containing air, dry nitrogen gas and a vacuum of 3 × 10^?5 mm of Hg. Spectra obtained at temperatures up to 500°K showed no dependence on the presence or absence of oxygen in the ambient atmosphere. The deresistance of pressed pellets of the polymer was measured in the temperature range 450°K to 525°K, and the results were described by the relation R = R₀c^E/kT. The activation energy E had a value of 1.2 ± 0.2 ev and the resistivity at 500°K was approximately 10¹³ ohm-em. The ESR signal is attributed to an intrinsic property of the polymer which is associated with a conjugated bond system along the polymer backbone. Neither the activation energy nor the magnitude of the resistivity suggest that the delocalized electrons associated with the conjugated bond system have produced unusual electrical characteristics in the polymer.     

Linear diacetylene polymers containing bis(dimethylsilyl) phenyl and/or bis-(tetramethyldisiloxane) carborane residues: Their synthesis,characterization and thermal and oxidative properties

A series of inorganic-organic linear diacetylenic hybrid polymers ( 5a–e ) were prepared by the polycondensation reaction of 1,4-dilithiobutadiyne with 1,4-bis(dimethylchlorosilyl)benzene and/or 1,7-bis(tetramethylchlorodisiloxane)-m-carborane. Their structures were characterized using FTIR, and ¹³C and ¹H NMR spectroscopies, and their thermal and oxidative properties were evaluated by DSC and TGA analyses. The hybrid polymers exhibited solubility in common organic solvents and were viscous liquids or low melting solids at room temperature. Broad prominent exotherms, attributed to reaction of the diacetylenic units, were observed by DSC in the 306°C to 354°C temperature range. When 5a–e were analyzed by TGA to 1000°C under nitrogen, weight retention between 79 and 86% were obtained. Ageing studies, performed at elevated temperatures in air on a thermoset and a ceramic obtained from polymer 5b , showed this system to have excellent thermal and oxidative stability. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2387–2391, 1997     

Preparation of a Star Network PEG-based Gel Polymer Electrolyte and Its Application to Electrochromic Devices

A star network polymer with a pentaerythritol core linking four PEG-block polymeric arms was synthesized, and its corresponding gel polymer electrolyte based on lithium perchlorate and plasticizers EC/PC with the character being colorless and highly transparent has been also prepared. The polymer host was characterized and confirmed to be of a star network and an amorphous structure by FTIR, ^1H NMR and XRD studies. The polymer host hold good mechanical properties for pentaerythritol cross-linking. Maximum ionic conductivity of the prepared polymer electrolyte has reached 8.83 × 10 ^-4 S·cm^-1 at room temperature. Thermogravimetry （TG） of the polymer electrolyte showed that the thermal stability was up to at least 150 ℃. The gel polymer electrolyte was further evaluated in electrochromic devices fabricated by transparent PET-ITO and electrochromically active viologen derivative films, and its excellent performance promised the usage of the gel polymer electrolyte as ionic conductor material in electrochrornic devices.     

An oxyluminescence investigation of the auto-oxidation of nylon 66

The kinetics of the thermal oxidation of stabilised and unstabilised nylon 66 fibres and films have been studied by photon counting oxyluminescence methods from 50°C to 150°C. The activation energies for initiation (E₁), propagation (E₃) and termination (E₅) over this temperature range are: E₁ = 16 kcal mol^?1, E₃ = 17·5 kcal mol^?1 and E₅ ≈ 12 kcal mol^?1. The extent of orientation of the polymer does not change the nature of the oxyluminescence curve or E₃ and E₅ above 110°C.Significant losses of critical mechanical properties of the fibres occur in the induction period at 100°C and non-stationary kinetics are described to enable this region to be studied by oxyluminescence. The oxidation rate in the induction period and the limiting rate region in air is one-third the rate in oxygen at atmospheric pressure. Non-stationary methods show that alkyl radical reactions are competitive with alkyl peroxy radical formation in air over the temperature range 100°C to 140°C. This affects the course of the oxidation reaction and the stabiliser efficiency and explains the observation of unsaturated oxidation products by phosphorescence spectroscopy.     

High temperature phosphorylated or nonphosphorylated laminating resins based on maleimido-substituted aromatic s-triazines

Several new phosphorylated or nonphosphorylated maleimide or nadimide systems containing s-triazine rings were synthesized. Their synthesis was accomplished by simple methods utilizing readily available and relatively inexpensive starting materials. All polymer precursors were characterized by infrared (IR) and proton nuclear magnetic resonance (¹H-NMR) spectroscopy. They were thermally polymerized to heat-resistant laminating resins. Thermal characterization of monomers and their cured resins was achieved using differential thermal analysis (DTA), dynamic thermogravimetric analysis (TGA) and isothermal gravimetric analysis (IGA). The cured resins were stable up to 304–330°C both in nitrogen and air atmospheres and formed anaerobic char yield 49–59% at 800°C. The phosphorylated polymers showed a lower temperature of initial weight loss but afforded higher anaerobic char yield than did the corresponding nonphosphorylated polymers. The thermal properties of the polymers were correlated with their chemical structure.     

Characterization and preparation of nanocrystalline MgCuZn ferrite powders synthesized by sol–gel auto-combustion method

Nanocrystalline Mg–Cu–Zn ferrite powders were successfully synthesized through nitrate–citrate gel auto-combustion method. Characterization of the nitrate–citrate gel, as-burnt powder and calcined powders at different calcination conditions were investigated by using XRD, DTA/TG, IR spectra, EDX, VSM, SEM and TEM techniques. IR spectra and DTA/TGA studies revealed that the combustion process is an oxidation–reduction reaction in which the NO₃ ⁻ ion is oxidant and the carboxyl group is reductant. The results of XRD show that the decomposition of the gel indicated a gradual transition from an amorphous material to a crystalline phase. In addition, increasing the calcination temperature resulted in increasing the crystallite size of Mg–Cu–Zn ferrite powders. VSM measurement also indicated that the maximum saturation magnetization (64.1 emu/g) appears for sample calcined at 800 °C while there is not much further increase in M _s at higher calcination temperature. The value of coercivity field (H _c) presents a maximum value of 182.7 Oe at calcination temperature 700 °C. TEM micrograph of the sample calcined at 800 °C showed spherical nanocrystalline ferrite powders with mean size of 36 nm. The toroidal sample sintered at 900 °C for 4 h presents the initial permeability (μ _i) of 405 at 1 MHz and electrical resistivity (ρ) of 1.02 × 10⁸ Ω cm.     

Synthesis of polyamides by ring-opening polyaddition of benzobis[1,2]oxazinediones with aliphatic diamines

Novel oxime-containing polyamides have been prepared by the ring-opening polyaddition of combinations of two benzobis[1,2]oxazinediones, 4,6-diphenylbenzo[1,2-d:5,4-d′]bis[1,2]oxazine-1,9-dione and 4,9-diphenylbenzo[1,2-d:4,5-d′]bis[1,2]oxazine-1,6-dione, with two aliphatic diamines in a polar aprotic solvent such as N-methyl-2-pyrrolidone. The polymerization was almost completed within a day at room temperature. These polymers had inherent viscosities in the range of 0.12–0.38 and were soluble in a wide range of solvents, including formic acid and hot m-cresol, as well as a number of polar aprotic solvents. All the polymers softened at a temperature ranging from 165 to 185°C. Thermal characterization of the polyamides by TGA and DTA showed polymer decomposition temperatures of about 240°C in air.     

Soluble and fusible polyamides and polyimides containing pyrazoline moieties and their crosslinking to heat-resistant resins

3-(4-Aminophenyl)-5-(3-aminophenyl)-2-pyrazoline as well as the 1-acetyl- or 1-benzoyl-substituted derivatives of this compound were synthesized and used for preparing a new series of polyamides and polyimides. Characterization of polymers was accomplished by inherent viscosity, ¹H-NMR, ¹³C-NMR, x-ray, DTA, TMA, TGA, and isothermal gravimetric analysis. The properties of polymers were correlated with their chemical structures. They were amorphous or microcrystalline and soluble in polar aprotic solvents, CCl₃COOH, and m-cresol. The polyamides showed an excellent solubility being soluble even in o-dichlorobenzene, 1,2-dichloroethane, and chloroform. The polymers displayed T_g at 127–163°C and softening at 150–195°C. The polyamide bearing unsubstituted pyrazoline moieties was remarkably more hydrophilic than those containing 1-acetyl- or 1-benzoyl-substituted pyrazoline segments. Upon curing, crosslinked polymers were obtained and their thermal stability was evaluated. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1353–1361, 1997     

A novel route to perovskite lead titanate from lead and titanium glycolates via the sol–gel process

Pure perovskite lead titanate powder (PbTiO₃) is successfully produced via the sol–gel process using lead and titanium glycolates as starting precursors and has been synthesized by the oxide one spot synthesis process. The obtained lead titanate is of the tetragonal form of the perovskite phase, with high purity and nearly zero moisture content. From high‐resolution mass spectra, the XRD technique, Raman‐FTIR and TGA‐DTA analysis, the lead–titanium glycolates undergo sol–gel transition through the formation of Pb? O? Ti bonds. From the SEM micrographs, the PbTiO₃ particle shape transforms from an agglomerate sphere to a needle and fiber‐like shapes as the calcination temperature is varied above T_c. The corresponding molecular structural transformation, from the tetragonal form to the cubic form, occurs at 430 °C. The lead titanate powder calcined at 300 °C for 3 h has the highest dielectric constant and electrical conductivity values, namely 17470 and 1.83 × 10^?3, respectively. Copyright © 2006 John Wiley & Sons, Ltd.     

Electrical and mechanical properties of the zone-drawn polypyrrole films

The zone-drawing method (ZD) was applied to electrochemically synthesized polypyrrole films containing tosylate (PPy/TsO) and the mechanical and electrical properties of the resulting films were investigated. It was found that the electrical conductivity of the zone-drawn film reached 365 S cm⁻¹ in the drawing direction, which was 4.7 times that of the original film. The tensile properties of the zone-drawn film were improved and Young's modulus and strength at break increased to 4.32 GPa and 90.1 MPa from 0.53 GPa and 40.4 MPa of the as-synthesized film, respectively. The dynamic storage modulus (E) increased by the zone-drawing over a whole experimental temperature range and attained 7.0 GPa at room temperature and 4.0 GPa even at 200°C. © 1996 John Wiley & Sons, Inc.     

Preparation and Properties of Novel Cyclophosphazenes Containing Cyanato Groups

Abstract

Novel cyclotriphosphazenes containing cyanato group (PZCN) derivatives were synthesized by a substitution reaction of 4-hydroxyphenoxycyclotriphosphazenes and cyanogen bromide (BrCN) in the presence of triethylamine (TEA). The PZCNs were characterized by FT-IR, liquid chromatography–mass spectrometry (LC-MS), ¹H NMR, ¹³C NMR, and ³¹P NMR spectroscopy. Curing reactions of the PZCNs were evaluated by FT-IR spectroscopy, thermogravimetry/differential thermal analysis (TG/DTA), and differential scanning, calorimetry (DSC). The PZCNs exhibited an exothermic peak due to curing within the temperature range of 140–300°C by DSC. The PZCNs were completely cured at 220°C. The cured PZCNs exhibited high thermal stability up to 350°C, a high char-forming capability, and electrical properties, such as dielectric constants (Dks) between 2.68 and 2.87, and dissipation factors (Dfs) between 0.008 and 0.013 at 1 MHz.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.     

A highly conductive and crystalline graphite-like polymer from 2,4-hexadiyn-1,6-diol

Poly-(2,4-hexadiyn-1,6-diol) (PHDO), prepared by NbCl₅/(n-Bu)₄Sn catalyzed metathesis of HDO, was pyrolyzed at various temperatures and electrical and structural properties of resulting polymers were investigated by FT-IR, Laser Raman, CP/MAS ¹³C-NMR and X-ray diffraction methods. The polymer obtained by pyrolysis of PHDO at 800°C showed a conductivity of about 10 S/cm at room temperature. The structure of the polymer seems to be a graphite-like crystal consisting of condensed aromatic layers. © 1994 John Wiley & Sons, Inc.     

Some electrical properties of wood pulp treated with sodium hydroxide

The effect of the degree of crystallinity and degree of polymerization on the electrical properties of soda-treated wood pulp has been investigated. The dielectric constant (E′) and the dielectric loss (E″) were measured for the treated samples over a frequency band 0.2–10 MHz at 20°C. Also, the electrical conductivity (σ) was calculated from the measured data of the dielectric constant. From the results obtained we found that the degree of crystallinity and the degree of polymerization decrease with time of oxidation while the number of carboxylic groups increased. E″,E′, and σ were found to increase with the decrease in the degree of crystallinity.