Synthesis and thermal stability,dielectric, and conductivity characteristics of some carbazole-bearing pendant and backbone sulfones

A group of poly(N-vinylcarbazole) pendant polysulfones has been prepared by reacting it with benzene, toluene, p-chlorobenzene- and p-nitrobenzenesulfonyl chloride and N-methyl carbazole, 3,6-disulfonyl chloride by the Friedel Crafts reaction. Carbazole-based backbone polysulfones have also been prepared by the reaction of N-methyl carbazole, 3,6-disulfonyl chloride and biphenyl, naphthalene, anthracene, and carbazole in presence of anhydrous aluminum chloride. The various sulfone polymers, thus prepared, have been structurally characterized by elemental analysis and IR spectroscopy. Detailed analyses of thermal stability, dielectric, and conductivity characteristics have revealed certain significant differences between these two types of sulfone polymers.     

Synthesis and thermal stability,dielectric, and conductivity characteristics of polymers with pendant and backbone anthracene sulfonyl groups

Anthracene-mono- and disulfonyl derivatives of polystyrene and poly (N-vinylcarbazole) have been prepared and the thermal stability, dielectric, and conductivity of these polymer pendant sulfones have been evaluated. The anthracene-based benzene, naphthalene, anthracene, and biphenyl copolysulfones have also been prepared and characterized in regard to the above-cited properties. Interesting variations in these properties between these two classes of polymers carrying pendant and backbone sulfonyl groups have been noted and rationalised from structural considerations.     

Thermal stability,morphological, dielectric,and conductivity characteristics of pyrrole modified poly-N-vinyl carbazole

N-vinyl-Carbazole (NVC) has been polymerized in the presence of pyrrole (PY) by anhydrous ferric chloride. The copolymer has been characterized by IR Spectroscopy. Thermal stability of P(PY–NVC) is intermediate between that of PNVC and PPY, respectively. DSC reveals a single glass transition break at 180–200°C for P(PY–NVC), which is higher than the T_g for polypyrrole (～ 165°C), but is lower than that for PNVC (～ 227°C). The XRD analysis reveals PPY to be totally amorphous and shows the percent crystallinity for P(PY–NVC) to be less than that of PNVC. Dielectric constants of the polymers follow the trend: PPY > P(PY–NVC) > PNVC, and fall sharply with the applied frequency to a limiting value. The polymers are characterized by a broad dielectric relaxation. DC conductivity is dependent on temperature and FeCl₃/polymer mole ratio and at a particular temperature follows the trend: PPY > P(PY–NVC) > PNVC. © 1993 John Wiley & Sons, Inc.     

Thermal stability,dielectric and conductivity characteristics of 9,10-anthracene-diol-anhydride polycondensates

Summary Four polycondensates have been prepared from 9,10-anthracene-diol and succinic anhydride, phthalic anhydride, pyromellitic dianhydride and 1,4,5,8-naphthalene tetracarboxylic dianhydride. Thermal stabilities, dielectric and conductivity characteristics of these condensates indicate that these properties are influenced by the nature of the anhydride moiety.     

Synthesis and thermal stability of hybrid fluorosilicone polymers

Aromatic hybrid fluorosilicones, such as perfluorocyclobutane aromatic polyethers, have higher thermal stability than typical polysiloxanes. While these polyethers decompose by homolytic cleavage of the oxygen-perfluorocyclobutane bond, the enhanced thermal stability of the polyethers may, in part, arise from this oxygen through the anomeric effect. To determine the effect of the ether oxygen on thermal stability, two perfluorocyclobutane aromatic units, one with and one without the oxygen, were modeled. To confirm the results experimentally, a series of hybrid fluorosilicones based on the latter were synthesized by thermocyclodimerization of 1-bromo-4-(trifluorovinyl)benzene, metal-halogen exchange, and condensation with one of 1,3-dichlorotetramethyldisiloxane; 1,7-dichlorooctamethyltetrasiloxane; or chlorine-terminated poly(dimethylsiloxane). The degradation temperature (T_1%) was lower (∼240 °C) than the comparable polyethers (∼430 °C). These results demonstrate the importance of the ether oxygen to the stability of perfluorocyclobutane aromatic polyethers through a number of effects including the anomeric effect and enhancing the strength of the silicon-aromatic bond.     

Silacyclobutane-functionalized cyclosiloxanes as photoactive precursors for high thermal stability,low dielectric constant and low dielectric loss polymers

Low dielectric photoactive materials have significant potential as components in future microelectronics. Although a number of photosensitive groups have been used to construct photopatternable materials, it remains challenging to introduce these groups into polymer chains via facile yet controlled polymerization techniques. The present work demonstrates the synthesis of a new class of photoactive cyclosiloxane monomers having hybrid siloxane-carbosilane main chains. These compounds can be cured by applying ultraviolet radiation and heat to promote the reaction of the silacyclobutene units and form hyper-cross-linked cyclosiloxanes. The cured resins show high thermal stability (with T_5% values in the range of 460–550°C), low dielectric constants (2.36–2.76 at 10 MHz) and low dielectric losses (10⁻³ at 10 MHz). Thus, these polymers could possibly be used as high-performance dielectric materials.     

Synthesis,characterization, thermal stability,conductivity, and band gap of a new aromatic polyether containing an azomethine as a side

In this study, the oxidative polycondensation reaction conditions of 4‐[(4‐methylphenyl)iminomethyl]phenol (4‐MPIMP) were studied by using oxidants such as air O₂, H₂O₂, and NaOCl in an aqueous alkaline medium between 50 and 90°C. The structures of the synthesized monomer and polymer were confirmed by FTIR, UV–vis, ¹H–¹³C‐NMR, and elemental analysis. The characterization was made by TGA‐DTA, size exclusion chromatography (SEC), and solubility tests. At the optimum reaction conditions, the yield of poly‐4‐[(4‐methylphenyl)iminomethyl]phenol (P‐4‐MPIMP) was found to be 28% for air O₂ oxidant, 42% for H₂O₂ oxidant, and 62% for NaOCl oxidant. According to the SEC analysis, the number–average molecular weight (M_n), weight–average molecular weight (M_w), and polydispersity index values of P‐4‐MPIMP were found to be 4400 g mol^?1, 5100 g mol^?1, and 1.159, using H₂O₂, and 4650 g mol^?1, 5200 g mol^?1, and 1.118, using air O₂, and 5100 g mol^?1, 5900 g mol^?1, and 1.157, using NaOCl, respectively. According to TG analysis, the weight losses of 4‐MPIMP and P‐4‐MPIMP were found to be 85.37% and 72.19% at 1000°C, respectively. P‐4‐MPIMP showed higher stability against thermal decomposition. Also, electrical conductivity of the P‐4‐MPIMP was measured, showing that the polymer is a typical semiconductor. The highest occupied molecular orbital and the lowest unoccupied molecular orbital energy levels and electrochemical energy gaps (E) of 4‐MPIMP and P‐4‐MPIMP were found to be ?5.76, ?5.19; ?3.00, ?3.24; 2.76 and 1.95 eV, respectively. According to UV–vis measurements, optical band gaps (E_g) of 4‐MPIMP and P‐4‐MPIMP were found to be 3.34 and 2.82 eV, respectively. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Perfluorocyclobutane aromatic ether polymers. III. Synthesis and thermal stability of a thermoset polymer containing triphenylphosphine oxide

The preparation of a novel triaryl phosphine oxide thermoset polymer containing the perfluorocyclobutane linkage is described. The synthetic methodology involves the formation of a Grignard reagent from 4-bromotrifluorovinyloxybenzene and reaction with phosphorous trichloride to form the triaryl phosphine trifluorovinyl ether monomer. Oxidation of the phosphine monomer with hydrogen peroxide in ethanol provides quantitative conversion of the phosphine to the phosphine oxide. Analysis of the thermal decomposition of the resulting polymer in both nitrogen and air indicates improvement in thermal and thermal/oxidative stability with respect to the previously reported polymer prepared from 1,1,1-tris(4-trifluorovinyloxy)phenyl ethane. Differences in thermal and thermal/oxidative performance still exist, indicating that oxidative processes contribute to the polymer decomposition in air. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2005–2012, 1998     

Synthesis,characterization, and thermal behavior study of methyl methacrylate polymers containing 4‐carbazole substitutes

A new polymerizable monomer, [4‐(9‐ethyl)carbazolyl]methyl methacrylate ( 2 ), was synthesized by reacting of methacrylic acid and 4‐hydroxymethyl‐9‐ethyl carbazole ( 1 ) by esterification procedure in the presence of N,N′‐dicyclohexylcarbodiimide. The resulting monomer was then polymerized free‐radically to form the poly(methyl methacrylate) containing 4‐(9‐ethyl)carbazolyl pend ent groups. Also, copolymerization of monomer 2 with various acrylic monomers such as methyl methacrylate, ethyl methacrylate, methyl acrylate, ethyl acrylate, and n‐butyl acrylate by azobisisobutyronitrile as a free radical polymerization initiator gave the related copolymers in high yields. The structure of all the resulted compounds was characterized and confirmed by FTIR and ¹H NMR spectroscopic techniques. The average molecular weight of the obtained polymers was determined by gel permeation chromatography using tetrahydrofurane as the solvent. The thermal gravimetric analysis and differential scanning calorimeter instruments were used for studying of thermal properties of polymers. It was found that, with the incorporation of bulky 4‐(9‐ethyl)carbazolyl substitutes in side chains of methyl methacrylate polymers, thermal stability and glass transition temperature of polymers are increased. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4989–4995, 2006     

Measurements of the thermal conductivity and thermal diffusivity of polymers

In this paper, the thermal conductivity and thermal diffusivity of nine polymers were measured by using the transient short‐hot‐wire method. The corresponding specific heat was measured with a commercial Differential Scanning Calorimeter (DSC). The effects of temperature on the thermal conductivity, thermal diffusivity, and the product of density and specific heat are further discussed. The results show that the transient short‐hot‐wire method can be used to measure the thermal conductivity, thermal diffusivity, and the product of density and specific heat of polymers within uncertainties of 3%, 6%, and 9%, respectively.     

Thermal conductivity of some electron transfer polymers

A number of electron transfer polymers were prepared by reacting various α, ω-alkanediamines with benzoquinone. The resulting polymers, through the formation of inter and intramolecular complexes, displayed high thermal conductivity with a strong temperature dependency. The mechanism contributing to the increased thermal conductivity was attributed to strong interchain complexing.     

Flammability and thermal stability of isocyanate-based polymers

A series of model polyurethanes and polyureas, a polyamide, and a polyimide were prepared by reacting 4,4′-diphenylmethane diisocyanate or polyisocyanates having similar polybenzyl structures with aliphatic or aromatic coreactants. Thermogravimetric analyses indicated that the flammability of the polymers was related to the formation of volatile flammable products during early stages of decomposition. Determinations of the heat evolved during differential thermal analyses and of the thermodynamic heats of combustion suggested that the extent and rate of reaction were among the important factors governing flame propagation. Flame-resistant polymers were prepared by use of structural elements which were thermally stable and nonvolatile or which formed nonflammable decomposition products.     

On thermal conductivity of some fabrics

The apparent density and the thermal conductivity of some samples of different wool/terylene blends were measured. It was shown that by increasing the terylene percentage, both the apparent density and the overall thermal conductivity increase to a maximum, and then decrease again. The blend consisting of 50% wool and 50% terylene has the maximum values of both thermal conductivity and apparent density.     

Synthesis and electrophosphorescent device study of carbazole containing dendronized styrenic polymers

Styrenic polymers P1(G0-CZ) and P2(G2-CZ) with carbazoles and carbazole containing dendrons as side chains were efficiently synthesized via “graft-to” approach by using copper-catalyzed azide/alkyne cycloaddition (CuAAC) reaction. The new polymers showed wide band gaps and had good thermal stabilities. Two new polymers were studied as electrophosphorescent host materials in OLED devices. Electrophosphorescent devices with the configuration of ITO/PEDOT:PSS/polymers:Ir(ppy)₃/TPBI/LiF/Al were fabricated. The polymer P1(G0-CZ) based device showed a maximum current efficiency of 21.4 cd/A, a power efficiency of 12.7 lm/W and an external quantum efficiency of 6.02%. The effect of host polymer structures on the aggregation of transition metal complexes Ir(ppy)₃ in active layer was also investigated.     

Structural,thermal, dielectric and ac conductivity properties of lithium fluoro-borate optical glasses

Transparent and stable glasses in the chemical composition of Li₂O–LiF–B₂O₃–MO (M = Zn and Cd) have been prepared by a conventional melt quenching method. For these glasses, absorption spectra, structural (XRD, FT-IR, and Raman spectra), thermal (TG–DTA and DSC), dielectric (?′, ?″, tan δ), ac conductivity (σ_ac), and electric modulus (M′ and M″) have been investigated. Amorphous nature of these glasses has been confirmed from their XRD profiles. The LFB glasses with the presence of ZnO or CdO an extended UV-transmission ability has been achieved. The measured FT-IR and Raman spectra have exhibited the vibrational bands of B–O from [BO₃] and [BO₄] units and Li–O. The dielectric properties (tan δ, dielectric constant (?′), dielectric loss (?″)), electrical modulus and electrical conductivity (σ_ac) of these glasses have also been studied from 100 Hz to 1 MHz at the room temperature. Based on the trends noticed in the ac conductivities, the present glasses could be found useful as battery cathode materials.     

Kinetics of thermal degradation of liquid-crystalline aromatic polymers

SUMMARY: The kinetics of thermal degradation of thermotropic liquid-crystalline aromatic polymers under nitrogen and air was systematically investigated by dynamic thermogravimetry. The thermal degradation temperature and kinetic parameters such as activation energy, decomposition order and frequency factor, have been determined by three methods on the basis of a single heating rate measurement. The effect of polymer molecular structure, end group, testing atmosphere and calculatingethod on the characteristic temperatures, kinetic parameters, and lifetime have been discussed. The initial decomposition temperature and estimated lifetime for the most thermotropic aromatic polymers are above 420°C and larger than 26 days at 200°C or 2.3 hours at 300°C, respectively. Some theoretical explanations of variation of thermal and kinetic parameters have been proposed.     

Origin of dielectric response and conductivity of some alicyclic polyimides

High‐performance alicyclic‐containing polyimides for advanced applications, derived from 5‐(2,5‐dioxotetrahydrofurfuryl)‐3‐methyl‐3‐cyclohexene‐1,2‐dicarboxylic acid anhydride or bicyclo[2.2.2]oct‐7‐ene‐2,3,5,6‐ tetracarboxylic dianhydride and two flexible aromatic diamines, were synthesized by a classical two‐step polycondensation reaction. The dielectric spectra behavior over wide frequency and temperature ranges of 1 Hz‐1 MHz and –150°C÷+250°C, respectively, was investigated according to chemical and micro‐structural aspects. The dielectric constants have low values and are dependent on dianhydride flexibility and diamine links, in relation with the charge–transfer complex (CTC) and free volume, and, consequently, with packing of the polymer chains and polarizable groups per volume units. All polyimide films develop two relaxation processes, i.e., γ and β relaxation, involving different enthalpy and entropy contributions induced by their chemical structures. Frequency–temperature‐dependent conductivity showed that conductivity increased with frequency and also that energy bandgap representation could be suitable for explaining the temperature influence on AC‐conductivity. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Liquid crystalline polymers, 9. Synthesis and thermal behavior of some oligomers containing a diethyletheric spacer

Polyethers based on bis(2-chloroethyl) ether and various bisphenols were obtained using a phase transfer catalysis technique in a liquid/liquid system. 4,4′-Dihydroxyazobenzene, 4,4′-dihydroxybiphenyl, bisphenol A, 2,7-dihydroxynaphthalene and 4,4′-dihydroxydiphenyl) sulfide were used. Only the polymers with azobenzene and biphenyl units exhibited mesophases, since the others have semi-crystalline or amorphous structures. The polymers were characterized by ¹H NMR, DSC and optical microscopy in polarized light. The molecular weights of the samples were low, situated in the oligomeric domain. The various transfer rates of the bisphenols from the aqueous to the organic phase, in some cases, led to very different copolymerization ratios as compared to the feed ratios. The LC polymers exhibited monotropic mesophases, probably for conformational reasons. A comparison between similar polyether structures containing the diethyletheric spacer and an oxetanic one was effectuated.     

Chemical modification of polypyrrole. II. Thermal stability,dielectric, and conductivity characteristics of polypyrrole substituted with phthalic and pyromellitic dianhydride

Polypyrrole (PPY) was electrophilically polycondensed with phthalic anhydride (PA) and pyromellitic dianhydride (PMDA). PPY–PA and PPY–PMDA polycondensates were evaluated in regard to their thermal stability and dielectric and conductivity behavior. The overall thermal stability is in the order PPY < PPY–PA < PPY–PMDA, which may be rationalized in terms of intra- and intermolecularly cross-linked structures of the polycondensates. IR spectral analyses of PPY–PA and PPY–PMDA subjected to heating at 300, 400, 500, and 550°C, respectively, were conducted to understand some of the structural changes in the polymer matrices. Both PPY–PA and PPY–PMDA exhibit high dielectric constants (200 and 125) at low frequency (10³ Hz), which fall monotonically with increasing frequency, suggesting the possibility of interfacial polarization. The conductivity values of PPY–PA and PPY–PMDA are in the range 10^?3–10^?4 ohm^?1 cm^?1, which are conspicuously lower than that for unmodified PPY (2.5). This is due to the adverse effect of incresing temperature on the PPY chain stability, whereby structural conjugation and eventually conductivity will be affected. © 1994 John Wiley & Sons, Inc.