Effect of ammonia on the temperature‐dependent conductivity and thermopower of polypyrrole

We report the first measurements of the effect of ammonia gas on the temperature dependence of the conductivity and thermoelectric power of polypyrrole films. Our data are for samples of very different conductivities, extending down to a temperature of 200 K for low‐conductivity polypyrrole gas sensors, and down to 4.2 K for more highly‐conducting PPy(PF₆) samples. We demonstrate that (except for the most metallic case) our polypyrrole samples show greater sensitivity to ammonia as the temperature is lowered (i.e. the fractional reduction in conductivity is greater at lower temperatures). Remanent decreases in conductivity are present after the removal of ammonia for higher pressure exposures, and remanent increases in the metal‐like thermoelectric power for the PPy(PF₆) for samples grown at higher temperatures. Our results indicate that the mechanism of this conductivity decrease in PPy(PF₆) is that ammonia causes a reduction in the size of metallic regions as disordered barrier regions are thickened. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1331–1338, 2006     

Frequency‐dependent conductivity of interpenetrating polymer network composites of polypyrrole–poly(vinyl acetate)

The frequency‐dependent conductivity of interpenetrating polymer network composites of polypyrrole (PPy) and poly(vinyl acetate) (PVAc) synthesized by FeCl₃‐impregnated PVAc films being dipped into solutions of pyrrole in water was investigated over a frequency range of 100 Hz to 2 MHz and a temperature range of 110–300 K. For specimens with a PPy content less than the percolation threshold, the quantum mechanical tunneling of electrons was the conduction mechanism. For specimens with a higher PPy content, correlated barrier hopping of electrons appeared to be operative. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1935–1941, 2001     

Tubular polypyrrole synthesized by in situ doping polymerization in the presence of organic function acids as dopants

Tubular polypyrrole (PPy) could be synthesized by in situ doping polymerization in the presence of β‐naphthalene sulfonic acid (NSA) as dopant. The resultant tubular PPy–NSA not only exhibits high room temperature conductivity (ς_RT = 10 S/cm) but is also soluble in m‐cresol. The molecular structure of PPy–NSA is identical to the characteristic structure of PPy synthesized by a conventional method. It has been demonstrated that NSA dopant with large molecular size and plate–lebe structure is a key factor to control formation of tubular PPy–NSA. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1443–1449, 1999     

DC electrical conduction and morphological behavior of counter anion‐governed genesis of electrochemically synthesized polypyrrole films

Highly conducting polypyrrole (PPY) films, doped with various anions [pTS^?, ClO₄^?, and NO₃^? and mixed electrolyte system (pTS^? + ClO₄^?)], have been electrochemically synthesized in aqueous solution at ～275 K in an inert atmosphere. PPY exhibits metallic order dc conductivity at room temperature and shows variation of conductivity with respect to time of polymerization. Effect of dopant anion on growth mechanism of PPY is evident from its surface morphology. X‐ray photoelectron spectroscopy (XPS), used to examine the surface composition and doping level of various PPY films, confirms the anionic doping into the polymer backbone. Both XPS and ultraviolet–visible spectroscopy give evidence of formation of polarons and bipolarons. The temperature (4.2–320 K)‐dependent dc conductivity data of these PPY films have been explained by Mott's 3D variable‐range hopping conduction model. Mott's parameters have been estimated, and structural disorder with doping is correlated for all the samples. Mott's criterion for distant hopping sites prevails in case of moderately doped samples (PPY3, PPY4, and PPY5), whereas the hopping to nearest neighbor sites is found more suitable in case of highly doped samples (PPY1 and PPY2). The origin of these changes is due to the modification in the molecular structure of PPY, which is governed by different growth mechanisms for organic (pTS^?) and inorganic (ClO₄^? and NO₃^?) counter anions. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Electronic conductivity of pyrrole and aniline thin films polymerized by plasma

In this article, we present a study of the influence of temperature and humidity on the electric conductivity of polyaniline and polypyrrole thin films doped with iodine and synthesized by plasma (PAn/I and PPy/I, respectively). The polymers presented the characteristic ohmic conduction mechanism via electrons; however, the conductivity was much lower than that presented by the polymers obtained by traditional chemical oxidation. We submitted the polymers to heating–cooling cycles to study the temperature dependence of the conductivity. During the heating stage of the cycles, the electric conductivity of PPy/I showed a strong dependence on the humidity content. However, during the cooling step, the plots of conductivity, as a function of the inverse temperature of PPy/I and PAn/I, showed typical Arrhenius behavior. The activation energy of PPy/I had an average value of 1.1 ± 0.1 eV and was independent of the reaction time, whereas PAn/I presented a more complex behavior with activation energies that depended on the reaction time and the regional crystallinity induced in the heating step of the cycles. All the activation energies were below 2 eV, which places them in the semiconductor regime. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 3247–3255, 2000     

Paper: An effective substrate for the enhancement of thermoelectric properties in PEDOT:PSS

A novel strategy via paper as an effective substrate has been introduced as a thermoelectric material in this work. Free‐standing poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)/paper composite films are conveniently prepared by a one‐step method of directly writing PEDOT:PSS solution on paper, making the process simple, rapid, and facile. The free‐standing composite films display excellent flexibility, light weight, soaking stability in water, and great potential in large‐scale production. Improved thermoelectric properties are obtained in PEDOT:PSS/paper composite films, owing to the simultaneously enhanced Seebeck coefficient (30.6 μV K^?1) and electrical conductivity, and a low thermal conductivity (0.16 W m^?1 K^?1) compared with pristine PEDOT:PSS films. The results indicate that paper as an effective substrate is suitable for the preparation of high‐performance and flexible thermoelectric materials. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 737–742     

Small‐angle X‐ray scattering from poly(methylmethacrylate) in aqueous solutions of t‐butyl alcohol

Segment‐segment interaction of poly(methylmethacrylate) in t‐butyl alcohol‐water mixtures in poor solvent regime was studied. From the small‐angle X‐ray scattering measurements of semidilute solution range, the binary and ternary cluster integrals of polymer segments were determined from concentration dependence of the correlation length at various temperatures just above the upper critical solution temperature. We have calculated the contributions of the segment–segment interaction to the entropy and enthalpy from the measured temperature dependence of these interaction parameters and found that both quantities are negative and decrease with decreasing t‐butyl alcohol content. FT‐IR absorption peak of carbonyl group of poly(methylmethacrylate) shifts to the lower frequency with increasing water content. The implications of these findings are discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2195–2199, 1999     

The preparation of polyaniline/polypyrrole conductive polymer films on polycarbonate‐coated Pt electrodes

In this study, free‐standing polymer films were obtained first with an electrochemical coating of polyaniline and then with a coating of polypyrrole on an insulating polycarbonate‐coated Pt electrode. The films contained varying amounts of polyaniline and polypyrrole obtained by varying the electrolysis time, and their conductivities were determined. The Raman spectra of the films taken from the electrode side were similar to those of pure polyaniline, whereas the spectra of the solution side were identical to those of pure polypyrrole. The resistance change in the films between −15 and +120°C revealed that the films were sensitive to temperature. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 51–59, 2000     

Study of a plasticized‐unoriented P(VF2/VF3) (73/27 mol%) copolymer. I. The effects of crystallization conditions on morphology,physical, and thermal properties

The results of a study on the effects of a plasticizer, tricresyl phosphate, on the mechanical and thermal properties of unoriented films of poly(vinylidene fluoride–trifluoroethylene) (VF₂/VF₃) copolymer (73/27 mol%) are presented. Films were prepared by both quenching and slow‐cooling from the melt with plasticizer concentrations of 0, 5, and 10% by weight. For the slow‐cooled films, a reduction in crystallinity by 25% was observed for the heavily plasticized films, together with a reduced dynamic mechanical modulus (≈ 58%) and an increased dielectric constant (≈ 200%). For the quenched films, a small increase in crystallinity was observed together with a reduced modulus and an increased dielectric constant. Measurements of the temperature dependence of the modulus and dielectric constant at 10 Hz. were also carried out from −100°C to 100°C. This data showed that for slow‐cooled films the glass transition temperature decreased from −28°C to ‐52°C at the highest doping level. DSC thermal analysis shows a decrease in the Curie transition (≈ 4°C) and melting temperatures (≈ 9°C) for the quenched films, while the slow‐cooled films only showed a decrease in melting temperature (≈ 10°C), while the Curie transition temperature was unaffected. In addition, evidence of a two‐phase system or a nonferroelectric crystal phase is noted by the presence of two Curie transition temperature peaks. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 19–28, 1999     

Click chemistry‐based synthesis of azo polymers for second‐order nonlinear optics

Four linear polymers containing pendant azo moiety were synthesized through click chemistry for second‐order nonlinear optical study. The polymers were found soluble in most of the polar organic solvents such as tetrahydrofuran (THF), chloroform, and dimethyl formamide (DMF). The polymers showed thermal stability up to 300 °C and glass transition temperatures (T_g) in the range of 120–140 °C. The molecular weights (M_w) of these polymers (measured by gel permeation chromatography) were in the range 37,900–55,000 g/mol. The polymers were found to form optically transparent films by solution casting from THF solution. Order parameters were calculated from UV–vis absorption spectra. The morphology changes in the films after poling were characterized by atomic force microscopy. The angular dependence, temperature dependence, and time dependence of second harmonic generation (SHG) intensity were obtained by using 1064 nm Nd:YAG laser. The SHG intensity remained unchanged up to 95 °C. At room temperature, it remained stable up to 8 days after initial drop of about 14%. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis and characterization of novel polyimides with bulky pendant groups

New dianhydrides containing t‐butyl and phenyl pendant groups have been synthesized and used as monomers, together with commercial diamines, to prepare novel polyimides. The influence of the chemical structure of the monomers on their reactivity has been studied by quantum semiempirical methods. The polyimides have been characterized by FTIR and by NMR in the case of soluble polymers. The presence of pendant groups and the method used to imidize polyimide precursors greatly affected polymer properties such as solubility, glass transition temperature, thermal stability, and mechanical properties. As a rule, the novel polyimides showed better solubility in organic solvents than the parent polyimides. Glass transition temperatures in the range 250–270°C and decomposition temperatures over 520°C were observed for the set of current polymers. Tensile strengths up to 135 MPa and mechanical moduli up to 3.0 GPa were measured on films of the current polyimides. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 805–814, 1999     

Synthesis and properties of novel sulfonated polyimides containing 1,5‐naphthylene moieties

A series of novel sulfonated polyimides (equivalent weight per sulfonic acid = 310–744 g/equiv) containing 10–70 mol % 1,5‐naphthylene moieties were synthesized as potential electrolyte materials for high‐temperature polymer electrolyte fuel cells. The polycondensation of 1,4,5,8‐naphthalene tetracarboxylic dianhydride, 4,4′‐diamino‐2,2′‐biphenyldisulfonic acid, and 1,5‐diaminonaphthalene gave the title polymer electrolytes. The polyimide electrolytes were high‐molecular‐weight (number‐average molecular weight = 36.0–350.7 × 10³ and weight‐average molecular weight = 70.4–598.5 × 10³) and formed flexible and tough films. The thermal properties (decomposition temperature > 260 °C, no glass‐transition temperature), stability to oxidation, and water absorption were analyzed and compared with those of perfluorosulfonic acid polymers. The polyimide containing 20 mol % 1,5‐naphthylene moieties showed higher proton conductivity (0.3 S cm^?1) at 120 °C and 100% relative humidity than perfluorosulfonic acid polymers. The temperature and humidity dependence of the proton conductivity was examined. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3901–3907, 2003     

Thermal transporting properties of electrically conductive polyaniline films as organic thermoelectric materials

Thermal transporting properties of electrically conductive polyaniline films were first investigated in wide range of temperatures above room temperature as organic thermoelectric materials. Thermal conductivities of various protonic acid-doped polyaniline films were measured by combination of a laser flash method and a differential scanning calorimeter in relation with electrical conductivity and a kind of dopant. The thermal conductivities thus measured are in the range of conventional organic polymers, indicating that the doped polyaniline films have extremely low thermal conductivities among electrically conductive materials, and have correlation with neither electrical conductivity, nor a kind of dopant. Consequently the polyaniline film, which shows very high electrical conductivity, has comparable thermoelectric figure-of-merit (ZT) with feasible inorganic thermoelectric materials such as iron silicide. This revised version was published online in August 2006 with corrections to the Cover Date.     

Synthesis and properties of new polyarylates from 1,4‐bis(4‐carboxyphenoxy)naphthyl or 2,6‐bis(4‐carboxyphenoxy)naphthyl and various bisphenols

New 1,4‐naphthyl and 2,6‐naphthyl‐containing polyarylates having inherent viscosities up to 1.28 dL/g were synthesized by the high‐temperature solution polycondensation from the acid chloride of 1,4‐bis(4‐carboxyphenoxy)naphthyl or 2,6‐bis(4‐carboxyphenoxy)naphthyl and various bisphenols. Most of the resulting polyarylates showed amorphous characteristics and were readily soluble in common organic solvents such as N,N‐dimethylacetamide (DMAc), N‐methyl‐2‐pyrrolidone (NMP), o‐chlorophenol, and chloroform. Transparent, flexible, and colorless films of these polymers could be cast from the DMAc solutions. Their cast films had tensile strengths ranging from 54.9 to 84.2 MPa, elongations at break from 5.3% to 19.0%, and initial modulus from 2.0 to 2.8 GPa. These polymers had glass transition temperatures in the range of 172–280°C and began to lose weight around 400°C, with 10% weight loss being recorded at about 450°C in air. Dynamic mechanical analysis (DMA) reveals that the polyarylates containing isopropylidene linkages have three transitions on the temperature scale between −100 and 300°C. However, only two transitions were observed in the other polyarylates without isoproylidene linkage. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 645–652, 1999     

Synthesis and characterization of novel polybenzimidazoles bearing pendant phenoxyamine groups

A novel aromatic diacid, 3, 5‐dicarboxyl‐4′‐amino diphenyl ether, containing pendant phenoxy amine group was synthesized. Homo‐ and co‐polybenzimidazoles containing different content of pendant phenoxyamine groups were synthesized by condensation of 3,3′‐diaminobenzidine with this acid and a mixture of this acid and isophthalic acid in different ratio in polyphosphoric acid. Copolybenzimidazoles with structural variations were also synthesized based on this acid and pyridine dicarboxylic acid, terephthalic acid, adipic acid, or sebacic acid. The polymers have good solubility in polar aprotic solvents and strong acids and they form tough flexible films by solution casting. The polymers were characterized by different instrumental techniques (FTIR, TGA, DSC, XRD, etc.) and for solvent solubility, mechanical properties, inherent viscosity, and proton conductivity. The inherent viscosities of the polymers vary in the range of 0.62–1.52 dL/g. They have high thermal stability up to 475–506 °C (IDT) in nitrogen, high glass transition temperatures (T_g) ranging from 313 to 435 °C and good tensile strength ranging from 58 to 125 MPa. Proton conductivity of homo polymer is 3.72 × 10^?3 S/cm at 25 °C and 2.45 × 10^?2 S/cm at 200 °C © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5776–5793, 2008     

Dielectric relaxation processes in epoxy resin—ZnO composites

Polymer matrix‐ZnO microcomposites were prepared in different filler concentrations. The electrical relaxation dynamics of all samples was examined by means of broadband dielectric spectroscopy (BDS) over a wide temperature range. Two relaxation modes (namely β and γ), observed in the low temperature region, are attributed to the reorientation of small polar groups of the polymer matrix. Glass‐rubber transition (α‐mode) of the polymeric matrix and interfacial polarization phenomena are considered as responsible for the recorded relaxation processes in the high temperature region. An additional relaxation mode, named intermediate dipolar effect (IDE), is recorded at temperatures higher than ?30 °C in all composites. Its occurrence and dynamics are related to the presence and concentration of the filler. IDE and α‐relaxation are observed in the same frequency and temperature range, leading to a mutual superposition. The two processes were distinguished following a simulation procedure employing the simultaneous fitting of two Havrilliak‐Negami terms and a third term describing the contribution of DC conductivity to dielectric losses. The temperature dependence of relaxation times for α‐mode follows the Vogel‐Tamann‐Fulcher equation, whereas IDE relaxation times follow unusual temperature dependence. The latter is discussed under the assumption of intrinsic interfacial polarization phenomena within ZnO crystal domains. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 445–454, 2009     

Glassy polymer‐sorption phenomena measured with a quartz crystal microbalance technique

The quartz crystal microbalance (QCM) method is applied to the measurement of CO₂ sorption in glassy poly(ethylene terephthalate) (PET), poly(methyl methacrylate), and polysulfone. Polymer thin films in the thickness range of 350–550 nm are prepared by spin‐casting onto the quartz crystal devices. Sorption isotherms at temperatures below the glass transition are analyzed with the dual‐mode sorption model. As‐cast, quenched, and slow‐cooled thermal‐conditioning protocols yield consistent trends in the sorption level, namely, as‐cast > quenched > slow‐cooled. The sorption levels and model results for the quenched‐conditioned samples measured with QCM compare favorably with those reported from the pressure‐decay and gravimetric methods on thick films. With extended analysis of PET, the QCM technique is also useful for the exploration of the temperature dependence associated with gas sorption in glassy polymer systems. Measured heats of sorption and the collapse of the Langmuir component near the PET glass‐transition temperature agree with those reported previously. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2109–2118, 2003     

Synthesis and characterization of new fluorene‐based poly(ether imide)s

A novel bis(ether anhydride) monomer, 9,9‐bis[4‐(3,4‐dicarboxyphenoxy)phenyl]fluorene dianhydride (4), was synthesized from the nitrodisplacement of 4‐nitrophthalonitrile by the bisphenoxide ion of 9,9‐bis(4‐hydroxyphenyl)fluorene (1), followed by alkaline hydrolysis of the intermediate tetranitrile and dehydration of the resulting tetracarboxylic acid. A series of poly(ether imide)s bearing the fluorenylidene group were prepared from the bis(ether anhydride) 4 with various aromatic diamines 5a–i via a conventional two‐stage process that included ring‐opening polyaddition to form the poly(amic acid)s 6a–i followed by thermal cyclodehydration to the polyimides 7a–i. The intermediate poly(amic acid)s had inherent viscosities in the range of 0.39–1.57 dL/g and afforded flexible and tough films by solution‐casting. Except for those derived from p‐phenylenediamine, m‐phenylenediamine, and benzidine, all other poly(amic acid) films could be thermally transformed into flexible and tough polyimide films. The glass transition temperatures (T_g) of these poly(ether imide)s were recorded between 238–306°C with the help of differential scanning calorimetry (DSC), and the softening temperatures (T_s) determined by thermomechanical analysis (TMA) stayed in the range of 231–301°C. Decomposition temperatures for 10% weight loss all occurred above 540°C in an air or a nitrogen atmosphere. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1403–1412, 1999     

Secondary doping in poly(3,4‐ethylenedioxythiophene):Poly(4‐styrenesulfonate) thin films

The electrical and structural properties of poly(3,4‐ethylenedioxythiophene):poly(4‐styrenesulfonate) (PEDOT:PSS) thin films deposited from aqueous dispersion using different concentrations of selected secondary dopants are studied in detail. An improvement of the electrical conductivity by three orders of magnitude is achieved for dimethyl sulfoxide, sorbitol, ethylene glycol, and N,N‐dimethylformamide, and the secondary dopant concentration dependence of the conductivity exhibits almost identical behavior for all investigated secondary dopants. Detailed analysis of the surface morphology and Raman spectra reveals no presence of the secondary dopant in fabricated films, and thus the dopants are truly causing the secondary doping effect. Although the ratio of benzenoid and quinoid vibrations in Raman spectra is unaffected by doping, the phase transition in PEDOT:PSS films owing to doping is confirmed. Further analysis of temperature‐dependent conductivity reveals 1D variable range hopping (VRH) charge transport for undoped PEDOT:PSS, whereas highly conductive doped PEDOT:PSS films exhibit 3D VRH charge transport. We demonstrate that the charge ‐ hopping dimensionality change should be a fundamental reason for the conductivity enhancement. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1139–1146     

Synthesis and characterization of poly(arylene ether sulfone) copolymers with sulfonimide side groups for a proton‐exchange membrane

A sulfonimide‐containing comonomer derived from 4,4′‐dichlorodiphenylsulfone was synthesized and copolymerized with 4,4′‐dichlorodiphenylsulfone and 4,4′‐biphenol to prepare sulfonimide‐containing poly(arylene ether sulfone) random copolymers (BPSIs). These copolymers showed slightly higher water uptake than disulfonated poly(arylene ether sulfone) copolymer (BPSH) controls, but their proton‐conductivity values were very comparable to those of the BPSH series with similar ion contents. The proton conductivity increased with the temperature for both systems. For samples with 30 mol % ionic groups, BPSI showed less temperature dependence in proton conductivity and slightly higher methanol permeability in comparison with BPSH. The thermal characterization of the sulfonimide copolymers showed that both the acid and salt forms were stable up to 250 °C under a nitrogen atmosphere. The results suggested that the presumed enhanced stability of the sulfonimide systems did not translate into higher protonic conductivity in liquid water. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6007–6014, 2006