Influence of the dopant on the polypyrrole moisture content: Effects on conductivity and thermal stability

Having in mind to produce electrically conductive carbon–epoxy composite materials, we have filled an insulating epoxy resin with an electronic conducting polymer, polypyrrole (PPy). To select the PPy that best suits this process, various PPys were chemically synthesized. The syntheses were performed in water via a dispersion polymerization route using, initially, either FeCl₃ (PPy–Cl⁻) or (NH₄)₂S₂O₈ (PPy–HSO₄⁻) as oxidizing agents. Then, using (NH₄)₂S₂O₈ as the oxidant, two other PPy doped with aromatic species were obtained due to the dissolution of paratoluenesulfonic acid (PPy–TS⁻) or naphtalenesulfonic acid (PPy–NS⁻) in the reaction media. The characterization of the PPy samples by conductivity measurements, together with elemental and thermal analysis, showed that PPy–TS⁻ exhibits the highest conductivity and thermal stability, with the conductivity remaining steady over 14 days. In addition, a stabilizing effect of the aromatic anions was observed. The experiments have shown that moisture in the PPy cannot be entirely removed and that, with increasing moisture content, the conductivity also increases, indicating an ionic conductivity superimposed on the electronic conductivity usually observed in PPy. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1567–1577, 1998     

聚吡咯纳米线的合成及热稳定性研究

以阳离子表面活性剂十六烷基三甲基溴化铵(CTAB)为软模板,磷酸(PA)、苯甲酸(BA)和乙酸(EA)为掺杂剂,通过化学氧化法合成了直径为40～90 nm的聚吡咯(PPy)纳米线,通过热重分析(TGA)系统地研究了有机酸(BA,EA)、无机酸(PA)、CTAB和PA的浓度以及反应温度对PPy纳米线热稳定性的影响,同时对形成机理进行了探讨。结果表明,刚性结构的有机酸和多元无机酸掺杂的PPy纳米线的热稳定性最好。     

Epoxy/benzoxazinyl POSS nanocomposite resin with low dielectric constant and excellent thermal stability

Benzoxazinyl modified polyhedral oligomeric silsesquioxane (BZPOSS) is successfully synthesized and used to prepare nanocomposites with bisphenol A type epoxy resin (E51). The differential scanning calorimetry results showed the curing peak temperature of E51/BZPOSS blend decrease to 242°C, suggesting the high catalytic activity of BZPOSS to the polymerization of E51. The scanning electron microscope micrographs of poly(E51/BZPOSS)s and silicon element distribution maps given by EDS both demonstrated homogeneous dispersion of BZPOSS. Dielectric properties tests confirmed the dielectric constant can be reduced by the introduction of BZPOSS, which is attributed to the nano-pores from the cage structure of POSS. When 20 wt% BZPOSS was added, the dielectric constant decreased to 2.28 at 1 MHz. Meanwhile, DMA and TGA results indicated the thermal stability and heat resistance of poly(E51/BZPOSS)s at high temperature increased with the increase of BZPOSS, which is due to the increase of the crosslinking density and the change of crosslinking structure of copolymer.     

Synthesis,characterization, and conductivity studies of polypyrrole/copper sulfide nanocomposites

Nanocomposites of polypyrrole (PPy) containing copper sulfide (CuS) were synthesized by an in situ chemical oxidative polymerization. The nanocomposites were characterized by FTIR, SEM, XRD, DSC, TGA, and conductivity studies. The FTIR spectra ascertained the chemical interlinking of polypyrole with metal sulfide nanoparticles. Morphological analysis showed that the nanoparticles were uniformly covering the entire substrate. The XRD pattern reveals that the nanoparticle incorporated polypyrrole showed a crystalline nature and the crystallinity of the polymer increases with increase in concentration of CuS nanoparticles. From DSC, an increase in glass transition temperature shows the increased orderness in the polymer composite than in the pure polypyrrole. Thermal analysis (TGA) of the composite showed a progressive increase in the thermal stability with increase in content of CuS. The frequency dependent electrical properties (a.c. conductivity) of the nanocomposites were higher than that of polypyrrole. The d.c. electrical conductivity increased with increase in amount of nanoparticles in the polymer matrix. The results obtained for these composites have greater scientific and technological interest. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effect of dopant type on the properties of polyaniline

The comparative study on the effect of different type of dopants on the properties of polyaniline (PANI) is relative less although dopant has profound effect of the properties of PANI. So, the aim of the present work is to study the effect of different type of dopant, namely strong inorganic hydrochloric acid (HCl), organic and aromatic acids containing different aromatic substitution, namely p‐toluene sulfonic acid (PTSA), dodecylbenzenesulfonic acid (DBSA), organic and aliphatic acids having long hydrocarbon chain, namely lauric acid (LA), on the properties of PANI. The PANI was prepared through oxidative polymerization methods and doped with HCl, PTSA, DBSA, and LA and then characterized through different methods like conductivity measurement, UV, X‐ray, DSC, TGA, and SEM. It was found that the properties of doped PANI depend on the type and molecular size of the dopant. With the increase in dopant chain length, the crystallinity is decreased, whereas the d‐spacing, interchain separation, and solubility are increased. The bond formation of water molecules with the backbone nitrogen of the polymers is much less in presence of aromatic dopants when compared with those of inorganic or aliphatic dopants. All the doped polyanilines under investigation do not decompose up to 500°C. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis and properties of the water-soluble self-acid-doped polypyrrole: poly[4-(3-pyrrolyl)butanesulfonic acid]

The water-soluble polypyrrole, poly[4-(3-pyrrolyl)butanesulfonic acid] (P3PyBSH), in which the β-position of pyrrole ring is substituted with n-butanesulfonic acid group, is synthesized by oxidation polymerization of 3PyBSNa followed with an ion-exchange of Na⁺ with H⁺. It can be cast into free-standing film from its aqueous solution and has a conductivity of 4.0×10⁻⁴ S/cm, higher than that of its sodium salt (5.5× 10⁻⁶ S/cm) by about 2 orders. The increase in conductivity is attributed to the self-doping by the protons originally on the side chains as supported by the absence of the anion FeCl₄ ⁻ (which generates during the polymerization) and the presence of polaron and bipolaron characteristics in its UV-Vis and IR spectra.     

Rheological behavior ‐ Electrical and thermal properties of polypyrrole/graphene oxide nanocomposites

Polypyrrole/graphene oxide (Ppy/GO) nanocomposites were synthesized via in situ polymerization of pyrrole in the presence of GO at various proportions (1–5%). They were characterized to determine their electrical, thermal, and rheological properties by various techniques. The aim of this study was to determine the rheological behavior of Ppy/GO nanocomposite at different mass ratios (100 : 1, 100 : 2, 100 : 3, 100 : 4, and 100 : 5%) and temperature (25–180°C) using a rotational mode in cone‐plate method. The shear stress (τ Pa) and viscosity (η Pa s) values of the nanocomposites increased with the increase in GO mass ratio added to Ppy, which was accompanied by an increased flexibility of the nanocomposites due to the higher aspect ratio of the GO sheet. Hence, it is suggested that the GO sheets are effective for the reinforcement of Ppy thereby significantly improvising its thermal stability, electrical conductivity, and rheological properties. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40642.     

Characterization of polypyrrole/azocalix[4]arene salts: Electrical properties and thermal stability

Polypyrrole (PPy) was doped with the azocalix[4]arene [(5,11,17,23‐tetrakis[(p‐carboxyphenyl)azo]25,26,27,28‐tetrahydroxycalix[4]arene)] host species. PPy/azocalix[4]arene salts were characterized by FTIR, TGA, SEM, X‐ray diffraction, and conductivity measurements. The properties of PPy were investigated in the presence of azocalix[4]arene host species. The conductivity of PPy increased in the presence of azocalix[4]arene. TGA results indicated that the PPy/azocalix[4]arene salts have higher thermal stability than PPy. It was observed from SEM analysis that the particle diameter of PPy decreased with increasing content of azocalix[4]arene. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of silanol on the thermal stability of poly[methyl(trifluoropropyl)siloxane]

Poly[methyl(trifluoropropyl)siloxane] (PMTFPS), which is an essential polymer in oil-resistant rubber materials, exhibits unsatisfactory thermal stability. In this article, PMTFPSs with methyl and hydroxyl terminal groups are prepared, and their thermal stabilities are investigated via thermogravimetric analysis and pyrolysis-gas chromatography-mass spectrometry in an inert atmosphere. Additionally, the degradation mechanisms are discussed in terms of molecular structural characteristics (bond length and bond angle) and reaction driven forces (electrostatic potential and atom charge) based on quantum chemistry calculations. PMTFPS is found to degrade mainly into cyclic monomers through (a) the Si O rearrangement reaction in the middle of the chain and (b) the “back-biting” reaction from the end of the chain. PMTFPS with silanol terminal groups is more likely to degrade according to pathway (b), resulting in more cyclotrisiloxane. Furthermore, the silanol from nano-silica accelerates the degradation of PMTFPS, and the mechanism of this process is presented.     

Shrinking rate of conducting grains in HCl–protonated polyaniline,polypyrrole, and polypyrrole/polyaniline blends with their thermal aging

The dc electrical conductivity (σ) of HCl‐protonated polyaniline, polypyrrole, and their blends was measured from 80 to 300 K for thermal aging times between approximately 0 and 600 h. The thermal aging took place at 70°C under room atmosphere. The change of σ with the temperature (T) and the decrease of σ with the thermal aging time (t) are consistent with a granular metal type structure, in which conductive grains are randomly distributed into an insulating matrix. Aging makes the grains shrink in a corrosion‐like process. From σ = σ(T) measurements the ratio s/d, where s is the average separation between the grains and d their diameter, as well as the rate d(s/d)/dt of their decrease with t were calculated. These revealed that the conductive grains consist of a shell, in which aging proceeds at a decreasing rate, and a central core, which is consumed at a much slower rate. Our measurements not only permitted the estimation of the shell thickness, which lies between 0 and 5 Å, but also gave quantitative information about the quality of the shells and the cores from their aging rates. The shells are consumed with an average rate of d(s/d)/dt = 6.6 × 10^?4 (h^?1), which is about 5 times greater than the more durable cores. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 117–122, 2005     

A high temperature polymer of phthalonitrile‐substituted phosphazene with low melting point and good thermal stability

A phthalonitrile‐substituted phosphonitrilic monomer has been synthesized from phosphonitrilic chloride trimer and then polymerized with addition of 4‐(hydroxylphenoxy)phthalonitrile (HPPN). The chemical structures of the phosphonitrilic monomer and polymer were characterized by Fourier Transform Infrared spectroscopy (FT‐IR) and proton Nuclear Magnetic Resonance spectroscopy (¹H NMR). Curing behaviors and thermal stabilities of the polymer were investigated through differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Analysis showed that the monomer has large processing temperature window and good thermal stability. Apparent activation energy, initial curing temperature (T_i), curing temperature (T_p), and termination curing temperature (T_f) of the phosphonitrilic polymer were explored. Dynamic mechanical analysis (DMA), glass transition temperature (T_g) were studied, and limiting oxygen index (LOI) were estimated from the van Krevelen equation, which indicates the polymer process high modulus and good flame retardance. Micro‐scale combustion calorimetry (MCC) was also used for evaluating the flammability of the polymers. Postcuring effects were explored, showing excellent thermal and mechanical properties with postcuring. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42606.     

Highly filled multilayer thermoplastic/graphene conducting composite structures with high strength and thermal stability for electromagnetic interference shielding applications

Polyvinyl chloride (PVC)/graphene and poly(methyl methacrylate) (PMMA)/graphene nanocomposites were made by solution casting technique with graphene weight fractions of 1, 5, 10, 15, and 20%. Multilayer structures of the composites were made by hot compression technique to study their electromagnetic interference shielding effectiveness (EMI SE). Tensile strength, hardness, and storage modulus of the nanocomposites were studied in relation with graphene weight fraction. There has been a substantial increase in the electrical conductivity and EMI SE of the composites with 15–20% filler loading. Differential thermal analysis of the composites shows improved thermal stability with an increase in graphene loading. PMMA/graphene composites have better thermal stability, whereas PVC/graphene composites have superior mechanical properties. About 2 mm thick multilayer structures of PMMA/graphene and PVC/graphene composites show a maximum EMI SE of 21 dB and 31 dB, respectively, in the X band at 20 wt % graphene loading. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47792.     

Studies on the curing behavior,thermal, and mechanical properties of epoxy resin-co-amine-functionalized lead phthalocyanine

A high performance copolymer was prepared by using epoxy (EP) resin as matrix and 3,10,17,24-tetra-aminoethoxy lead phthalocyanine (APbPc) as additive with dicyandiamide as curing agent. Fourier-transform infrared spectroscopy, dynamic mechanical analysis (DMA), differential scanning calorimetric analysis (DSC), and thermogravimetric analysis (TGA) were used to study the curing behavior, curing kinetics, dynamic mechanical properties, impact and tensile strength, and thermal stability of EP/APbPc blends. The experimental results show that APbPc, as a synergistic curing agent, can effectively reduce the curing temperature of epoxy resin. The curing kinetics of the copolymer was investigated by non-isothermal DSC to determine kinetic data and measurement of the activation energy. DMA, impact, and tensile strength tests proved that phthalocyanine can significantly improve the toughness and stiffness of epoxy resin. Highest values were seen on the 20 wt% loading of APbPc in the copolymers, energy storage modulus, and impact strength increased respectively 388.46 MPa and 3.6 kJ/m², T_g decreased 19.46°C. TGA curves indicated that the cured copolymers also exhibit excellent thermal properties.     

Novel Ni/polypyrrole and Cu/polypyrrole composites prepared in the presence of different acids: Synthesis and investigation of thermal stability

We report the synthesis and characterization of new organic/inorganic hybrid materials constituted of Ni(0) and Cu(0) nanoparticles and polypyrrole (PPy). Copper and nickel nanoclusters were synthesized by a chemical reduction of aqueous metal salt solutions by sodium borohydride. PPy/Ni(0) and PPy/Cu(0) composites were obtained in the presence of two different acids (H₃BO₃, CH₃COOH), by polymerizing pyrrole‐Ni and pyrrole‐Cu particles by using iron (III) chloride. The composites have been characterized by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and magnetic susceptibility techniques. Conductivity measurements of samples were taken using four‐probe devices. The PPy/Ni(0) and PPy/Cu(0) nanocomposites doped with different acids exhibited higher conductivity values than those of homopolymers. Among all samples, Ni/PPy‐H₃BO₃ has the highest conductivity (1.42 S cm^?1). Homopolymers and composites showed a stable and increasing conductivity with increasing temperature, except Ni(0). We observed that from TGA analysis of polymers, metal composites of PPy synthesized in two different media are more stable than those of PPy‐CH₃COOH and PPy‐H₃BO₃. The magnetic susceptibility values of homopolymers and Cu are negative, whereas the other samples are positive. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

The effect of pentaerythritol‐aluminum on the thermal stability of rigid poly(vinyl chloride)

Pentaerythritol‐aluminum (PE‐Al) was synthesized by a solid‐phase reaction in this study. The formation and characteristics of PE‐Al were confirmed by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). SEM images showed that the shapes of PE‐Al particles were spherical and the average size was around 23 nm. The thermal properties of rigid poly(vinyl chloride) (PVC) with PE‐Al were tested by Congo red test, thermal aging test, conductivity test, thermogravimetric analysis (TGA), and UV–visible spectroscopy test. The results showed that combination of PE‐Al, in comparison with commercial thermal stabilizers, presented an obvious improvement in stabilization efficiency of PVC. Moreover, addition of PE‐Al could significantly prolong static stability time of PVC, reduce weight loss, and improve the initial color of PVC films. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3704–3709, 2013     

Mechanical properties and thermal stability of poly(L‐lactide)/calcium carbonate composites

Poly(L ‐lactide) (PLA) was melt‐mixed with micrometer‐sized and nanosized calcium carbonate (CaCO₃) particles before and after modification with calcium stearate. Adhesion between the CaCO₃ particles and the PLA matrix was assessed qualitatively by scanning electron microscopy observation of the fractured surface morphology of the composites. The effect of the incorporation of the CaCO₃ particles on the thermal stability of the PLA‐based composites was quantified by the temperatures corresponding to 5 and 50% of weight loss and the activation energy determined through thermogravimetric analyses of the composites. The tensile strength and modulus values of the composite were improved greatly without a significant loss in the elongation at break when the nanosized CaCO₃ was incorporated up to 30 wt %. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

A comparative study of aging characteristics and thermal stability of oil palm ash,silica, and carbon black filled natural rubber vulcanizates

Filler‐filled natural rubber (NR) vulcanizates were prepared by conventional laboratory‐sized two roll mills and cured using sulfuric system. The effect of thermal aging on physical properties and thermogravimetric analysis (TGA) of oil palm ash (OPA) and commercial fillers (i.e., silica vulkasil C and carbon black N330)‐filled NR vulcanizates at respective optimum loading and equal loading were studied. Before aging, the OPA‐filled vulcanizates showed comparable optimum strength as carbon black‐filled vulcanizates. The hardening of aged filler‐filled NR vulcanizates happened after aging, thereby tensile strength and elongation at break reduced while the modulus increased. Fifty phr carbon black‐filled vulcanizates showed better retention in tensile properties as compared to silica (10 phr) and OPA (1 phr). This was attributed to the addition of different filler loading and this finding was further explained when equal loading of filler‐filled vulcanizates was studied. Fourier transform infra‐red analysis showed chemical structure had changed and tensile fractured surface exhibited smooth appearance due to the deterioration in tensile properties after aging. TGA also denoted the thermal stability was depending on the amount of filler loading. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4474–4481, 2013     

Assessment of mechanical performance,thermal stability and water resistance of novel conductive poly(lactic acid)/modified natural rubber blends with low loading of polyaniline

Biodegradable conductive polymer blends made from poly(lactic acid) (PLA), liquid natural rubber (LNR) and polyaniline (PANI) were prepared via a melt‐blending technique assisted by ultrasonic treatment. The effects of PANI at low loading (0.03 to 0.11 wt%) on the electrical conductivity and mechanical, thermal and physical properties of PLA/LNR/PANI blends were investigated. It was found that the mechanical properties of samples improved when PANI was introduced into PLA/LNR. Tensile results showed that the optimum loading of PANI was achieved at 0.07 wt% with an improvement of 8% in tensile strength compared to neat PLA/LNR. Although it was at low loading, the incorporation of PANI promoted an outstanding electrical conductivity to PLA/LNR blends. Thermal analysis of the PLA/LNR/PANI blends was conducted using differential scanning calorimetry and thermogravimetry. The thermal stabilities of the blends were improved markedly with the presence of PANI. Comparing to PLA/LNR, the incorporation of PANI component improved the resistance towards water absorption. Variable‐pressure scanning electron microscopy micrographs of PLA/LNR/PANI confirmed the good mixing of PANI with PLA/LNR and strong interaction networks among the PANI, PLA and LNR components. © 2018 Society of Chemical Industry     

Humidity sensitivity of polypyrrole and polypyrrole/SBA‐15 host–guest composite materials

Polypyrrole (PPY) and PPY/SBA‐15 host–guest composite materials have been prepared using chemical synthesis route and characterized by XRD, IR, N₂ adsorption–desorption isotherms, and SEM. The humidity sensitive properties (HSP) of this kind of materials have been studied by analyzing the variation curve of impedance as a function of relative humidity. It was found that the PPY/SBA‐15 host–guest composites materials exhibit better HSP than that of the corresponding pure PPY. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3301–3305, 2006     

Synthesis,characterization, and curing behavior of carborane‐containing benzoxazine resins with excellent thermal and thermo‐oxidative stability

Two benzoxazine precursors bearing carborane moiety ( 1 and 2 ) were designed and synthesized successfully by the Mannich reaction of corresponding carborane bisphenol ( 3 and 4 ) with aniline and formaldehyde in 1,4‐dioxane. The obtained precursors were characterized by using multiple spectroscopic techniques including GPC, FTIR, ¹H NMR, ¹³C NMR, and ¹¹B NMR. Nonisothermal DSC studies showed that precursor 1 owned lower apparent activation energies (E_a) than 2 . The optimum curing processes of benzoxazine precursors were also obtained on the basis of DSC data. TGA analyses manifested that the incorporation of carborane moiety endowed the obtained benzoxazine resins (cured 1 and 2 ) with excellent thermal stability and unique thermo‐oxidative stability. The T_d data showed that the initial degradation of both cured 1 and 2 under nitrogen and air was postponed to some extent owing to the shielding effect of carborane moiety on adjacent organic fragments. At higher temperature three‐dimensional polymer networks with B‐O‐B and B–C linkages were formed as chars by the reaction of carborane cage with atmospheric moisture, degradation products such as phenolic hydroxyl, and oxygen (under air). Under nitrogen this network hindered the motion of radicals formed at elevated temperature and thus inhibited further polymer degradation processes. While under air, the formed boron‐rich networks could hardly be further oxidized into carbon dioxide so that the carborane‐containing benzoxazine resins also showed very high char yields. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43488.