Journal of Polymer Science Part B: Polymer Physics

Cover image for Vol. 49 Issue 7

1 April 2011

Volume 49, Issue 7

Pages i–iv, 467–550

  1. Cover Image

    1. Top of page
    2. Cover Image
    3. Reviews
    4. Full Papers
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      Cover Image, Volume 49, Issue 7 (pages i–ii)

      Article first published online: 24 FEB 2011 | DOI: 10.1002/polb.22232

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      Polymer solar cells are a low-cost alternative to inorganic photovoltaics, but reaching commercially viable efficiencies is heavily dependent on understanding and control of the polymer blend morphology in the devices, no matter which polymer is used. On page 499 of this issue, Nichole Cates Miller and colleagues construct the eutectic phase diagram of blends of the polymer pBTTT and fullerene derivative PC71BM. The phase diagram explains why solar cells with 75-80 wt % fullerene perform best, since these blends have both electron- and hole-conducting phases at room temperature, ensuring clear charge-conduction pathways to the electrodes. In addition, the authors also show how to suppress intercalation of the fullerene between the polymer side chains using rapid thermal annealing. The cover is an optical microscopy image of the phase separation in a 1:1 pBTTT:PC71BM blend that has been annealed above the eutectic temperature.

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      Inside Cover, Volume 49, Issue 7 (pages iii–iv)

      Article first published online: 2 MAR 2011 | DOI: 10.1002/polb.22239

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      Dendrimers have several advantages over polymers for electronics, including separate control of the surface groups and the core, which allows the processing and optoelectronic properties to be changed independently. They can be used as host materials for phosphorescent light-emitting diodes, where energy is transferred to emissive guest molecules. Efficient materials with solution processability, sufficient thermal properties and wide bandgaps capable of transferring energy to blue-light-emitting guests have been elusive. On page 531 of this issue, Alan Sellinger and colleagues report solutionprocessable high bandgap hosts with carbazole-functionalized cyclic phosphazene cores. The materials are amorphous with high glass transition temperatures due to their 3D rigid architecture, which simplifies processing. In addition, the optical and electronic properties depend solely on the dendrons, which can be selected to produce highly efficient devices with blue through to red emission. Inside cover art by Dr. Zien Ooi.

  2. Reviews

    1. Top of page
    2. Cover Image
    3. Reviews
    4. Full Papers
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      Conducting polymers: Efficient thermoelectric materials (pages 467–475)

      Nidhi Dubey and Mario Leclerc

      Article first published online: 8 FEB 2011 | DOI: 10.1002/polb.22206

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      Thermoelectric systems are very effective in harvesting electricity from waste heat or heat sources with small gradients relative to environmental temperature. Indeed, thermoelectric materials turn heat into electricity without any moving parts and could therefore be a green option for everything from power generation to microprocessor systems. This review highlights the recent progress made in this area utilizing conducting polymers and related composites. In particular, studies on polymer/inorganic materials composites have revealed very good Seebeck coefficients and high electrical conductivities with relatively low thermal conductivities.

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      Structure—Property relationships for exciton transfer in conjugated polymers (pages 476–498)

      Trisha L. Andrew and Timothy M. Swager

      Article first published online: 24 FEB 2011 | DOI: 10.1002/polb.22207

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      Conjugated polymers (CPs) combine the optoelectronic properties of semiconductors with the mechanical properties and processing advantages of plastics. The sensitivity of their optical properties to their environment make them ideal materials for applications such as sensors, but a complete understanding of the mechanisms of energy migration in CPs is still lacking. Here, the photophysical properties of exciton transport in a series of poly(p-phenyl ethynylene)s is reviewed, with a particular focus on signal amplification capabilities.

  3. Full Papers

    1. Top of page
    2. Cover Image
    3. Reviews
    4. Full Papers
    1. The phase behavior of a polymer-fullerene bulk heterojunction system that contains bimolecular crystals (pages 499–503)

      Nichole Cates Miller, Roman Gysel, Chad E. Miller, Eric Verploegen, Zach Beiley, Martin Heeney, Iain McCulloch, Zhenan Bao, Michael F. Toney and Michael D. McGehee

      Article first published online: 24 FEB 2011 | DOI: 10.1002/polb.22214

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      Some polymer:fullerene blends used in bulk heterojunction solar cells, such as pBTTT blends with PC71BM, form bimolecular crystals due to fullerene intercalation between the polymer side chains. By using differential scanning calorimetry and 2D grazing incidence X-ray scattering with in-situ thermal annealing the pBTTT:PC71BM phase diagram is determined. In addition, it's also shown to be possible to suppress intercalation by heating the blends above the eutectic temperature.

    2. Mechanisms of large actuation strain in dielectric elastomers (pages 504–515)

      Soo Jin Adrian Koh, Tiefeng Li, Jinxiong Zhou, Xuanhe Zhao, Wei Hong, Jian Zhu and Zhigang Suo

      Article first published online: 24 FEB 2011 | DOI: 10.1002/polb.22223

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      Subject to a voltage, an actuator mechanically deforms. Piezo-based electromechanical actuators exhibit small actuation strains below 1%, while polymer-based actuators exhibit actuation strains of up to 30%. If an elastomeric polymer is prestretched, actuation strain of more than 100% is possible. Still, this strain magnitude is about 10 times smaller than its mechanical strain capacity of 1000%. Theoretical predictions identify the limiting mechanism as electromechanical instability, and how this limit may be overcome.

    3. Polymer-regulated pattern formation in pseudo-2D arrays of a fullerene derivative at the solution—Air interface (pages 516–522)

      Shani Eliyahu, Chunlai Ren, Igal Szleifer and Rachel Yerushalmi-Rozen

      Article first published online: 10 JAN 2011 | DOI: 10.1002/polb.22200

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      Self-assembly of nanoparticles (NPs) into nonclose-packed arrays is of interest for a variety of applications; of special interest is the assembly of photochemically active fullerene derivatives. Pattern formation in a mixture of fullerene NPs with a polymer brush at the solution—air interface was found to be dependent on the interactions of the surface brush with a polymer dissolved in the subphase. Modeling of the system shows that the concentration of the polymer in the subphases mediates the dimensions of the surface brush and consequentially the lateral depletion interactions in the mixture.

    4. Hydration-mediated effects of saccharide stereochemistry on poly(N-isopropylacrylamide) gel swelling (pages 523–530)

      Nurit Manukovsky, Avi Shpigelman, Ravit Edelman and Yoav D. Livney

      Article first published online: 24 FEB 2011 | DOI: 10.1002/polb.22212

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      Some microorganisms use small molecules, such as sugars, to stabilize proteins against denaturation. To study saccharide stereochemistry effects on macromolecules in aqueous solutions, the influence of three aldohexoses on the swelling of poly(N-isopropylacrylamide) hydrogels is examined. The same order of the sugars' magnitude of effect (galactose>glucose>mannose) emerged for both gel deswelling and concentration difference between gel and solution. The more hydrated the sugar, the worse a cosolvent it is for polymer, hence the greater deswelling and imbalance in concentrations.

    5. Solution processable high band gap hosts based on carbazole functionalized cyclic phosphazene cores for application in organic light-emitting diodes (pages 531–539)

      Mui Siang Soh, Sonsoles Amor Garcia Santamaria, Evan Laurence Williams, Marta Pérez-Morales, Henk J. Bolink and Alan Sellinger

      Article first published online: 3 JAN 2011 | DOI: 10.1002/polb.22197

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      Hybrid dendrimers offer a solution-processable alternative to polymers in organic light-emitting diodes (OLEDs). A new class of such dendrimers based on cyclic phosphazene cores have been prepared and used as host materials for blue and green OLEDs. The dendrimers are prepared in high yield from minimal step reactions, are soluble in common solvents for solution processing, are amorphous, and have excellent thermal properties necessary for this application.

    6. Radical-cured block copolymer-modified thermosets (pages 540–550)

      Erica M. Redline, Lorraine F. Francis and Frank S. Bates

      Article first published online: 3 JAN 2011 | DOI: 10.1002/polb.22196

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      A high degree of crosslinking makes thermoset plastics brittle and prone to fracture, limiting the applications of these otherwise very interesting materials. Amphiphilic block copolymers have been shown to be effective tougheners for epoxy-thermosets. Instead, the fracture resistance of radical-cured thermosets is not significantly improved by the addition of the block copolymers, as inherent differences in network formation and the presence of network defects in the chain growth polymerized plastics somehow inhibit the ability of the micelles to toughen these materials.

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