Polymers

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25 pages, 689 KiB

Open AccessArticle

Towards Extrusion of Ionomers to Process Fuel Cell Membranes

by Yannick Molmeret, France Chabert, Nadia El Kissi, Cristina Iojoiu, Regis Mercier and Jean-Yves Sanchez

Polymers 2011, 3(3), 1126-1150; https://doi.org/10.3390/polym3031126 - 19 Jul 2011

Cited by 15 | Viewed by 9170

Abstract

While Proton Exchange Membrane Fuel Cell (PEMFC) membranes are currently prepared by film casting, this paper demonstrates the feasibility of extrusion, a solvent-free alternative process. Thanks to water-soluble process-aid plasticizers, duly selected, it was possible to extrude acidic and alkaline polysulfone ionomers. Additionally, [...] Read more.

While Proton Exchange Membrane Fuel Cell (PEMFC) membranes are currently prepared by film casting, this paper demonstrates the feasibility of extrusion, a solvent-free alternative process. Thanks to water-soluble process-aid plasticizers, duly selected, it was possible to extrude acidic and alkaline polysulfone ionomers. Additionally, the feasibility to extrude composites was demonstrated. The impact of the plasticizers on the melt viscosity was investigated. Following the extrusion, the plasticizers were fully removed in water. The extrusion was found to impact neither on the ionomer chains, nor on the performances of the membrane. This environmentally friendly process was successfully validated for a variety of high performance ionomers. Full article

(This article belongs to the Special Issue Conductive Polymers)

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40 pages, 795 KiB

Open AccessArticle

Electrically Conductive Epoxy Adhesives

by Erol Sancaktar and Lan Bai

Polymers 2011, 3(1), 427-466; https://doi.org/10.3390/polym3010427 - 10 Feb 2011

Cited by 83 | Viewed by 24650

Abstract

Conductive adhesives are widely used in electronic packaging applications such as die attachment and solderless interconnections, component repair, display interconnections, and heat dissipation. The effects of film thickness as functions of filler volume fraction, conductive filler size, shape, as well as uncured adhesive [...] Read more.

Conductive adhesives are widely used in electronic packaging applications such as die attachment and solderless interconnections, component repair, display interconnections, and heat dissipation. The effects of film thickness as functions of filler volume fraction, conductive filler size, shape, as well as uncured adhesive matrix viscosity on the electrical conduction behavior of epoxy-based adhesives are presented in this work. For this purpose, epoxy-based adhesives were prepared using conductive fillers of different size, shape, and types, including Ni powder, flakes, and filaments, Ag powder, and Cu powder. The filaments were 20 μm in diameter, and 160 or 260 μm in length. HCl and H₃PO₄ acid solutions were used to etch and remove the surface oxide layers from the fillers. The plane resistance of filled adhesive films was measured using the four-point method. In all cases of conductive filler addition, the planar resistivity levels for the composite adhesive films increased when the film thickness was reduced. The shape of resistivity-thickness curves was negative exponential decaying type and was modeled using a mathematical relation. The relationships between the conductive film resistivities and the filler volume fractions were also derived mathematically based on the experimental data. Thus, the effects of surface treatment of filler particles, the type, size, shape of fillers, and the uncured epoxy viscosity could be included empirically by using these mathematical relations based on the experimental data. By utilizing the relations we proposed to model thickness-dependent and volume fraction-dependent conduction behaviors separately, we were able to describe the combined and coupled volume fraction-film thickness relationship mathematically based on our experimental data. Full article

(This article belongs to the Special Issue Conductive Polymers)

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16 pages, 1338 KiB

Open AccessArticle

Synthesis of Novel π-Conjugated Rod-Rod-Rod Triblock Copolymers Containing Poly(3-hexylthiophene) and Polyacetylene Segments by Combination of Quasi-Living GRIM and Living Anionic Polymerization

by Tomoya Higashihara, Cheng-Liang Liu, Wen-Chang Chen and Mitsuru Ueda

Polymers 2011, 3(1), 236-251; https://doi.org/10.3390/polym3010236 - 10 Jan 2011

Cited by 15 | Viewed by 10287

Abstract

The first successful synthesis of a new rod-rod-rod triblock copolymer, polyacetylene(PA)-b-poly(3-hexylthiophene)(P3HT)-b-PA could be synthesized by a combination of quasi-living Grignard metathesis (GRIM) and living anionic polymerization. We first confirmed that poly(4-tolyl vinyl sulfoxide) (PTVS), which is a soluble precursor [...] Read more.

The first successful synthesis of a new rod-rod-rod triblock copolymer, polyacetylene(PA)-b-poly(3-hexylthiophene)(P3HT)-b-PA could be synthesized by a combination of quasi-living Grignard metathesis (GRIM) and living anionic polymerization. We first confirmed that poly(4-tolyl vinyl sulfoxide) (PTVS), which is a soluble precursor for PA, could be synthesized by living anionic polymerization in THF at −78 °C, initiated with 3-methyl-1,1-diphenylpentyllithium as the initiator in the presence of in situ-generated lithium enolate. The molecular weights (MWs) and polydispersities (PDIs) were well controlled (MW = 5,200–27,000, PDI = 1.10–1.22), respectively. A coil-rod-coil triblock copolymer, PTVS-b-P3HT-b-PTVS, (6,000-12,500-6,000) could also be synthesized, initiated with a P3HT-based difunctional macroinitiator in the presence of lithium enolate. GPC-RALLS and ¹H NMR analyses confirmed a high degree of structural homogeneity of PTVS-b-P3HT-b-PTVS. A thermal transformation reaction of the polymer was carried out in the film state at 170 °C for 2 h to afford PA-b-P3HT-b-PA quantitatively, as monitored by TGA and FT-IR analyses. The optical and electronic properties as well as the morphological behavior of the block copolymers were investigated by UV-vis spectroscopy, conductivity measurement, and AFM observation. Full article

(This article belongs to the Special Issue Conductive Polymers)

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14 pages, 496 KiB

Open AccessArticle

Partially Fluorinated Sulfonated Poly(ether amide) Fuel Cell Membranes: Influence of Chemical Structure on Membrane Properties

by Ying Chang, Yeong-Beom Lee and Chulsung Bae

Polymers 2011, 3(1), 222-235; https://doi.org/10.3390/polym3010222 - 7 Jan 2011

Cited by 15 | Viewed by 10817

Abstract

A series of fluorinated sulfonated poly (ether amide)s (SPAs) were synthesized for proton exchange membrane fuel cell applications. A polycondensation reaction of 4,4’-oxydianiline, 2-sulfoterephthalic acid monosodium salt, and tetrafluorophenylene dicarboxylic acids (terephthalic and isophthalic) or fluoroaliphatic dicarboxylic acids produced SPAs with sulfonation degrees [...] Read more.

A series of fluorinated sulfonated poly (ether amide)s (SPAs) were synthesized for proton exchange membrane fuel cell applications. A polycondensation reaction of 4,4’-oxydianiline, 2-sulfoterephthalic acid monosodium salt, and tetrafluorophenylene dicarboxylic acids (terephthalic and isophthalic) or fluoroaliphatic dicarboxylic acids produced SPAs with sulfonation degrees of 80–90%. Controlling the feed ratio of the sulfonated and unsulfonated dicarboxylic acid monomers afforded random SPAs with ion exchange capacities between 1.7 and 2.2 meq/g and good solubility in polar aprotic solvents. Their structures were characterized using NMR and FT IR spectroscopies. Tough, flexible, and transparent films were obtained with dimethylsulfoxide using a solution casting method. Most SPA membranes with 90% sulfonation degree showed high proton conductivity (>100 mS/cm) at 80 °C and 100% relative humidity. Among them, two outstanding ionomers (ODA-STA-TPA-90 and ODA-STA-IPA-90) showed proton conductivity comparable to that of Nafion 117 between 40 and 80 °C. The influence of chemical structure on the membrane properties was systematically investigated by comparing the fluorinated polymers to their hydrogenated counterparts. The results suggest that the incorporation of fluorinated moieties in the polymer backbone of the membrane reduces water absorption. High molecular weight and the resulting physical entanglement of the polymers chains played a more important role in improving stability in water, however. Full article

(This article belongs to the Special Issue Conductive Polymers)

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23 pages, 734 KiB

Open AccessArticle

A Polyvinyl Alcohol-Polyaniline Based Electro-Conductive Hydrogel for Controlled Stimuli-Actuable Release of Indomethacin

by Tong-Sheng Tsai, Viness Pillay, Yahya E. Choonara, Lisa C. Du Toit, Girish Modi, Dinesh Naidoo and Pradeep Kumar

Polymers 2011, 3(1), 150-172; https://doi.org/10.3390/polym3010150 - 5 Jan 2011

Cited by 68 | Viewed by 15144

Abstract

Electro-conductive hydrogels based on poly(vinyl alcohol), crosslinked with diethyl acetamidomalonate as the hydrogel component, were engineered using polyaniline as the inherently conductive component, and fabricated in the form of cylindrical devices to confer electro-actuable release of the model drug indomethacin. The hydrogels were [...] Read more.

Electro-conductive hydrogels based on poly(vinyl alcohol), crosslinked with diethyl acetamidomalonate as the hydrogel component, were engineered using polyaniline as the inherently conductive component, and fabricated in the form of cylindrical devices to confer electro-actuable release of the model drug indomethacin. The hydrogels were characterized for their physicochemical and physicomechanical properties. Cyclic voltammetry was employed for electro-activity and conductivity analysis. Drug entrapment efficiency ranged from 65–70%. “ON-OFF” switchable drug release was obtained by periodically applying-removing-reapplying an electric potential ranging from 0.3–5.0 V for 60 seconds at hourly intervals and the cumulative drug release obtained ranged from 4.7–25.2% after four release cycles respectively. The electro-stimulated release of indomethacin was associated with the degree of crosslinking, the polymeric ratio and drug content. A Box-Behnken experimental design was constructed employing 1.2 V as the baseline potential difference. Thedevices demonstrated superior swellability and high diffusivity of indomethacin, in addition to high electrical conductivity with “ON-OFF” drug release kinetics via electrical switching. In order to investigate the electro-actuable release of indomethacin, molecular mechanics simulations using AMBER-force field were performed on systems containing water molecules and the poly(vinyl alcohol)-polyaniline composite under the influence of an external electric field. Various interaction energies were monitored to visualize the effect of the external electric field on the erosion of polyaniline from the co-polymeric matrix. This strategy allows the electro-conductive hydrogels to be suitably applied for controlled, local and electro-actuable drug release while sustaining a mild operating environment. Full article

(This article belongs to the Special Issue Conductive Polymers)

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9 pages, 2152 KiB

Open AccessArticle

Synthesis of Polypyrrole-Intercalated Grafted Zirconium Phosphate Films by Anodic Electrodeposition and Their Electrochemical Capacities

by Takahiro Takei, Qiang Dong, Yoshinori Yonesaki, Nobuhiro Kumada and Nobukazu Kinomura

Polymers 2011, 3(1), 1-9; https://doi.org/10.3390/polym3010001 - 23 Dec 2010

Cited by 6 | Viewed by 9239

Abstract

Ternary hybrid film composed of a-zirconium phosphate nanosheet, 1,2-bis(dimethylchlorosilyl)ethane and polypyrrole was prepared by anodic electrodeposition. In the hybrid film, ordered a-zirconium nanosheets with grafts by silylation lay down parallel to the substrate and the polypyrrole molecules were intercalated between the nanosheets. The [...] Read more.

Ternary hybrid film composed of a-zirconium phosphate nanosheet, 1,2-bis(dimethylchlorosilyl)ethane and polypyrrole was prepared by anodic electrodeposition. In the hybrid film, ordered a-zirconium nanosheets with grafts by silylation lay down parallel to the substrate and the polypyrrole molecules were intercalated between the nanosheets. The electrochemical measurements confirmed that the hybrid film indicated capacitive behavior and the redox activity increase by approximately 25%. Full article

(This article belongs to the Special Issue Conductive Polymers)

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13 pages, 606 KiB

Open AccessArticle

New Insight into Organic Metal Polyaniline Morphology and Structure

by Bernhard Wessling

Polymers 2010, 2(4), 786-798; https://doi.org/10.3390/polym2040786 - 17 Dec 2010

Cited by 54 | Viewed by 19377

Abstract

Polyaniline is known to be a true metal, though a nanometal. Previous experimental and theoretical evidence is reviewed. Two important structural features are presented, which have not publicly been discussed so far: (a) The formation of complexes between polyaniline and metals (Cu, Fe, [...] Read more.

Polyaniline is known to be a true metal, though a nanometal. Previous experimental and theoretical evidence is reviewed. Two important structural features are presented, which have not publicly been discussed so far: (a) The formation of complexes between polyaniline and metals (Cu, Fe, Zn, In, etc.) which are crucial for most practical applications of the organic metal, polyaniline; and (b) a model for the polyaniline chain structure within the smallest morphological unit, the roughly 10 nm primary particle. Full article

(This article belongs to the Special Issue Conductive Polymers)

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21 pages, 701 KiB

Open AccessArticle

Synthesis of Ethylene Glycol Dimethacrylate-Methyl Methacrylate Copolymers, Determination of their Reactivity Ratios, and a Study of Dopant and Temperature Effects on their Conductivities

by Ulku S. Ramelow and Sreedhar Pingili

Polymers 2010, 2(3), 265-285; https://doi.org/10.3390/polym2030265 - 26 Aug 2010

Cited by 31 | Viewed by 16476

Abstract

Ultraviolet radiation was used as a photochemical initiator to synthesize ethylene glycol dimethacrylate-methyl methacrylate copolymers. Infrared spectroscopy was used to calculate reactivity ratios and to identify the type of copolymerization. The reactivity ratios of EGDMA and MMA were calculated as 0.6993 and 1.8635, [...] Read more.

Ultraviolet radiation was used as a photochemical initiator to synthesize ethylene glycol dimethacrylate-methyl methacrylate copolymers. Infrared spectroscopy was used to calculate reactivity ratios and to identify the type of copolymerization. The reactivity ratios of EGDMA and MMA were calculated as 0.6993 and 1.8635, respectively. The effect of lithium perchlorate as a dopant on copolymer conductivity and conversion was studied. The addition of dopant increased the conductivity of copolymers. For copolymers containing 5% MMA in the feed, dopant increased conductivity about 775 times; when the MMA percentage was 20% in the feed, dopant increased conductivity about 100 times. As MMA percentage increases in the copolymer, the conductivity values decrease from the mS to the µS region. This is consistent with the fact that PMMA has a lower conductivity than PEGDMA. The conductivity change of homopolymers and copolymers at various temperatures were studied. Both MMA and EGDMA polymers and their copolymers show a minimum in their conductivity vs. temperature graphs, indicating that they first act as a conductor and after a minimum temperature, become semiconductors and can be used to control current in electrical devices by temperature change. The measurement of conductivity change with time provided a new way to follow the kinetics of polymer/dopant reactions. The activation energy of interaction with dopant was calculated as 31.52 kJ/mol for MMA/EGDMA copolymers; for PEGDMA alone it was 54.7 kJ/mol. Full article

(This article belongs to the Special Issue Conductive Polymers)

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11 pages, 415 KiB

Open AccessArticle

Fabrication of Extrinsically Conductive Silicone Rubbers with High Elasticity and Analysis of Their Mechanical and Electrical Characteristics

by Anjum Saleem, Lars Frormann and Alexandru Soever

Polymers 2010, 2(3), 200-210; https://doi.org/10.3390/polym2030200 - 10 Aug 2010

Cited by 41 | Viewed by 12922

Abstract

Conductive plastics are attracting more and more interest in electronics due to their light weight and inability to rust, which are common problems associated with metals. The field of conducting plastics is not new. Much work has been done to impart electrical conductivity [...] Read more.

Conductive plastics are attracting more and more interest in electronics due to their light weight and inability to rust, which are common problems associated with metals. The field of conducting plastics is not new. Much work has been done to impart electrical conductivity to mechanically strong polymers such as polypropylene, polycarbonate and epoxies, etc. However there is a need to fabricate more flexible and elastic conductive polymers such as conducting silicone rubbers for use in various applications. In this work silicone rubbers reinforced with conductive fillers have been fabricated for use as sensors in textiles to detect the resistance change produced by stretching or relaxing. The variations of electrical resistance have been investigated by stretching and releasing the strands of conductive rubbers as a function of time. Two types of silicone rubbers—addition cured and condensation cured—were compounded with different electrically conductive fillers, among which carbon fibers have shown the best results. The carbon fibers improved the electrical conductance of the rubbers, even in very low weight percentages. The increasing concentration of fillers decreases the elasticity of the rubber. In order to keep the original properties of silicones, the filler concentration was kept as low as possible to produce a significantly detectable signal. The fabricated compounds were analyzed for their mechanical properties by stress strain curves. Such materials find their applications in electronics, antistatic applications, sports and the automotive industry where they can be used as deformation sensors. Full article

(This article belongs to the Special Issue Conductive Polymers)

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15 pages, 1289 KiB

Open AccessArticle

Synthesis and Properties of 1,8-Carbazole-Based Conjugated Copolymers

by Tsuyoshi Michinobu, Haruka Osako and Kiyotaka Shigehara

Polymers 2010, 2(3), 159-173; https://doi.org/10.3390/polym2030159 - 30 Jul 2010

Cited by 32 | Viewed by 12069

Abstract

A new series of conjugated carbazole polymers based on the 1,8-carbazolylene unit was synthesized by the Pd-catalyzed polycondensation between the 1,8-diiodocarbazole derivative and various bifunctional counter comonomers. An alkyne spacer was found to be a key to increasing the molecular weight of the [...] Read more.

A new series of conjugated carbazole polymers based on the 1,8-carbazolylene unit was synthesized by the Pd-catalyzed polycondensation between the 1,8-diiodocarbazole derivative and various bifunctional counter comonomers. An alkyne spacer was found to be a key to increasing the molecular weight of the resulting polymers. All the obtained polymers showed good solubilities in the common organic solvents, and they were fully characterized by Gel permeation chromatography (GPC), and ¹H NMR and infrared (IR) spectroscopies. The UV-vis absorption and fluorescence spectra revealed the relationship between the chemical structure and effective conjugation length. The efficiency order of the carbazole connectivity was 2,7-carbazolylene > 1,8-carbazolylene > 3,6-carbazolylene. The electrochemical properties of these polymers suggested the relatively facile oxidation at ca. +0.5–0.7 V vs. Fc/Fc⁺ or a high potential as p-type semiconductors. The combination of the electrochemical oxidation potentials and the optical band gaps allowed us to estimate the HOMO and LUMO levels of the polymers. It was shown that the energy levels of the 1,8-carbazole-based conjugated polymers can be tunable by selecting the appropriate comonomer structures. Full article

(This article belongs to the Special Issue Conductive Polymers)

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Review

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14 pages, 552 KiB

Open AccessReview

Conduction and Electrostriction of Polymers Induced by High Electric Fields

by Markus Karahka and Hans Jürgen Kreuzer

Polymers 2011, 3(1), 51-64; https://doi.org/10.3390/polym3010051 - 27 Dec 2010

Cited by 9 | Viewed by 11229

Abstract

After reviewing the new physics and chemistry in high electrostatic fields we use density functional theory to show that in fields around 1.5 V/Å the bandgap of polythiophene reduces to zero leading to field-induced metallization. In poly(ethylene glycol), on the other hand, such [...] Read more.

After reviewing the new physics and chemistry in high electrostatic fields we use density functional theory to show that in fields around 1.5 V/Å the bandgap of polythiophene reduces to zero leading to field-induced metallization. In poly(ethylene glycol), on the other hand, such fields lead to giant electrostriction of over 20% in length. Lastly, we give two examples of field-induced polymerization: (1) the closure of sulfur molecules S_n at n = 8 is suppressed remaining linear up to n ~ 20. (2) This also happens to water which forms linear whiskers up to n ~ 11. Full article

(This article belongs to the Special Issue Conductive Polymers)

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