Journal of Polymer Science Part B: Polymer Physics

Cover image for Vol. 52 Issue 6

15 March 2014

Volume 52, Issue 6

Pages i–ii, 419–484

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      Cover Image, Volume 52, Issue 6 (pages i–ii)

      Version of Record online: 10 FEB 2014 | DOI: 10.1002/polb.23456

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      Polyimide gels in N-methyl-2-pyrrolidone (NMP) form birefringence in suitable solvents at a critical concentration, exhibiting a disorder–order phase transition, as presented on page 450 by Jie Dong, Chaoqing Yin, Yumei Zhang, and Qinghua Zhang. In the polyimide/NMP system, the weak strip-like texture is observed for the solution with 10 wt% concentration, and then optical birefringence becomes more obvious upon further increasing concentration. A strong optical planar texture with intense colors obviously appears for the gel at 13 wt% concentration, indicating the formation of a fully anisotropic phase. This phenomenon presents the gelation process and broadens the application of the gel-spinning method in the fabrication of high performance fibers.

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    1. Miscibility maps for polymer blends: Effects of temperature, pressure, and molecular weight (pages 419–443)

      Elian M. Masnada, Grégoire Julien and Didier R. Long

      Version of Record online: 18 DEC 2013 | DOI: 10.1002/polb.23436

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      Polymer blends exhibit complex phase behaviors with various kinds of phase transitions: lower critical solution transitions, case-I upper critical solution transitions, case-II upper critical solution transitions, or hour-glass-like phase diagrams. The pressure may have a stabilizing effect or a destabilizing one. Miscibility maps regarding the occurrence of the various kinds of phase transitions, as a function of the difference in the self-energies of the constituents and of their molecular weights, are calculated for different molecular weight ratios.

    2. Crosslinking PMMA: Molecular dynamics investigation of the shear response (pages 444–449)

      Kyoungmin Min, Meredith Silberstein and N. R. Aluru

      Version of Record online: 22 DEC 2013 | DOI: 10.1002/polb.23437

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      Crosslinking can fundamentally change the mechanical properties of a polymer. When lightly crosslinked, poly(methyl-methacrylate) (PMMA) is more ductile when mechanically loaded than linear PMMA, despite having a higher glass transition temperature. Here, molecular dynamics simulations are used to investigate conformational and energetic differences between linear PMMA and lightly crosslinked PMMA under shear deformation. While crosslinks have a minimal direct energy contribution to the system, they can alter how the main chains conform to macroscopic loading.

    3. Gel–sol transition for soluble polyimide solution (pages 450–459)

      Jie Dong, Chaoqing Yin, Yumei Zhang and Qinghua Zhang

      Version of Record online: 26 DEC 2013 | DOI: 10.1002/polb.23438

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      Gelation can be defined as a phenomenon by which a polymeric material undergoes a phase transition from a liquid to a solid state. An understanding of the gelation process is important for both theoretical and industrial considerations. Here, high performance fibers are fabricated via gel spinning with a polymer gel consisting of a copolyimide in N-methyl-2-pyrrolidone. Compared with fibers produced by the conventional wetspinning process, the polyimide fibers produced here exhibit a relatively high tensile strength and modulus.

    4. Correction of Doi–Edwards' Green function for a chain in a harmonic potential and its implication for the stress-optic rule (pages 460–469)

      Jay D. Schieber and Tsutomu Indei

      Version of Record online: 9 JAN 2014 | DOI: 10.1002/polb.23439

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      For polymer melts, it is well-established that there is a proportionality relationship between the stress and the refractive index tensors as long as the polymer chains are Gaussian; this linear relation is called the stress-optic rule. Here, a rigorous derivation for the statistics of a Gaussian chain trapped in a tube-like harmonic potential is given. The calculation shows that such a model violates the stress-optic rule if pressure on the tube wall is included in stress predictions.

    5. Temperature-dependent location of a weakly segregated block copolymer in binary blends of block copolymers (pages 470–476)

      Sang-Byung Park, Jung-guk Ha, Sei Kwang Hahn and Wang-Cheol Zin

      Version of Record online: 26 DEC 2013 | DOI: 10.1002/polb.23440

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      An increasing domain spacing with an increasing temperature is observed in binary blends composed of block copolymers with complementary volume fractions. This is interpreted as the delocalization of a weakly segregated asymmetric block copolymer from the interface to a domain at higher temperatures. In this study, the effect of a weakly segregated asymmetric block copolymer on the phase behavior is emphasized.

    6. Processing and properties of melt spun polylactide–multiwall carbon nanotube fiber composites (pages 477–484)

      Reza Rizvi, Lemuel Tong and Hani Naguib

      Version of Record online: 9 JAN 2014 | DOI: 10.1002/polb.23441

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      The process of melt spinning can impart shear-induced orientations in both the filler particles and the surrounding polymer matrix. This work reports on the processing, morphology, and thermal and mechanical properties of melt spun polylactide multiwall carbon nanotube composite fibers. The roles of various processing parameters on the final fiber structure are elucidated. A synergistic effect is observed when oriented filler particles impart preferential crystallization of composite fibers, resulting in enhanced mechanical properties compared to bulk processed composites.

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