Concentrated solutions of liquid-crystalline polymers

Sato, Takahiro; Teŕamoto, Akio

doi:10.1007/3-540-60484-7_3

Cited by 154 publications

(264 citation statements)

References 137 publications

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“…59 This value is, to the best of our knowledge, the highest among all synthetic helical polymers prepared so far and is comparable with those of biological triple-stranded helical polymers, such as collagen (160-180 nm) and schizophyllan (150-200 nm), and even stiffer than the double-stranded helical DNA (o60 nm) and xanthan (120 nm). 60 Previously, we reported that a preferred-handed helicity could be induced in dynamically racemic helical poly(phenylacetylene)s with functional pendant groups. For example, cis-transoidal poly(phenylacetylene)s bearing carboxy (21), 24,35,61,62 phosphonic (22) (Figure 5c).…”

Section: Helical Structure Determination Of Liquid Crystalline Helicamentioning

confidence: 98%

“…Recently, we found that a preferred-handed helical st-PMMA can be induced in toluene in the presence of optically active alcohols, such as (S)-or (R)-2-phenylethanol (38), resulting in an optically active gel, which showed a VCD in PMMA infrared regions. On addition of fullerenes, such as C 60 , helical st-PMMA traps fullerenes within its helical cavity to form an optically active peapod-like inclusion complex ( Figure 14). Interestingly, the induced helical structure of the st-PMMA/fullerene complex can be memorized after complete removal of chiral alcohols and the complex exhibited a similar VCD because of the original PMMA in infrared regions, as well as an induced CD in the encapsulated C 60 chromophore regions, although C 60 itself is achiral.…”

Section: Synthesis and Structures Of Helical Polymers E Yashimamentioning

confidence: 99%

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Synthesis and structure determination of helical polymers

Yashima

2010

Polym J

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During the last decade, remarkable progress in developing synthetic helical polymers with a controlled helical sense has been achieved. However, the exact helical structures of most of the already prepared synthetic helical polymers remain unsolved. In this review, the recent progress in the synthesis of helical polymers and their structural determination, including helical pitch and handedness based on X-ray diffraction and spectroscopic measurements, together with high-resolution atomic force microscopy, is described. Polymer Journal (2010) 42, 3-16; doi:10.1038/pj.2009 Keywords: atomic force microscopy; circular dichroism; helical polymer; helical structure; X-ray diffractionThe helix is a unique structure as observed in nature from microscopic to macroscopic levels and is inherently chiral. Inspired by biological helices, such as DNA and proteins, chemists have been challenged to synthesize helical polymers with a controlled helical sense that aims not only to mimic biological helical structures but also to develop chiral materials for the separation of enantiomers and asymmetric catalysis. [1][2][3][4][5][6][7][8][9][10][11][12] The history of synthetic helical polymers with optical activity extends back to the 1960s when Pino and Lorenzi 13 investigated the structural and chiroptical properties of isotactic vinyl polymers prepared by the polymerization of a-olefins bearing optically active substituents. Although helical polyolefins are totally dynamic in nature and consist of short helical segments separated by frequently occurring helical reversals among disordered, random coil conformations, 14 this study was significant in the field of synthetic helical polymers, from which a number of helical polymers have been synthesized.On the basis of the pioneering studies by Nolte et al., 15 Okamoto et al. 16 and Green et al., 17 the existing synthetic helical polymers that exhibit an optical activity solely because of their macromolecular helicity can be classified into two categories with respect to their helix inversion barriers, that is, static and dynamic helical polymers (Figure 1). 9,12 Optically active helical polymers, such as poly(triphenylmethyl methacrylate) (1), 16 poly(t-butyl isocyanide) (2) 15 and polychloral (3), 18 have a sufficiently high helix inversion barrier and belong to the family of static helical polymers. Therefore, these helical polymers with either a right-or left-handed helix can be prepared by the helix-sense-selective polymerization of the corresponding achiral monomers using chiral catalysts or initiators under kinetic control. On the other hand, dynamic helical polymers, such as polyisocyanates (8) 17 and polysilanes (9), 19 possess a very low helix inversion barrier.As a consequence, they consist of interconvertible right-and lefthanded helical segments separated by rarely occurring helical reversals, as demonstrated by Green et al.,6,20,21 so that a preferred-handed helical conformation can be induced in the presence of a small amount of chiral residues at the pendant 6 or ter...

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Section: Helical Structure Determination Of Liquid Crystalline Helicamentioning

confidence: 98%

Section: Synthesis and Structures Of Helical Polymers E Yashimamentioning

confidence: 99%

Synthesis and structure determination of helical polymers

Yashima

2010

Polym J

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“…The entropy driven phase transition of monodisperse suspensions of purely repulsive rods from an isotropic to an aligned nematic phase has been extensively studied experimentally [1,2], theoretically [3,4], and computationally [5]. Binary mixtures of hard particles of different aspect ratios and/or shape can exhibit a much richer phase behavior.…”

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“…However, the topology of the theoretical phase diagram of binary mixtures of rods, including the progression of the phase behavior from a totally miscible nematic to a demixed N-N state and the related existence of N-N critical points, is a subject of considerable debate as the predicted phase behavior of the more concentrated phases (N-N and I-N-N) is extremely sensitive to the approximations employed [8,9,12,13,14]. The focus of past experimental studies has been on binary mixtures of rods of varying length where I-N, I-N-N and N-N coexistence have been measured [2,15,16,17].…”

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Nematic Phase Transitions in Mixtures of Thin and Thick Colloidal Rods

et al. 2005

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We report experimental measurements of the phase behavior of mixtures of thin (charged semiflexible fd virus) and thick (fd-PEG created by covalently grafting poly-(ethylene glycol) to the surface of fd virus) rods. The fd-PEG are sterically stabilized but the fd virus are charged, thus varying the ionic strength of a mixture of fd and fd-PEG varies the effective diameter of the bare fd rods, and the effective diameter ratio (d ≡ D fd-PEG /D fd ). We examine the phase diagrams of the rod mixtures and find isotropic-nematic, isotropic-nematic-nematic and nematic-nematic coexisting phases with increasing concentration. In stark contrast to predictions from earlier theoretical work, we observe a nematic-nematic coexistence region bound by a lower critical point. Moreover, we show that a rescaled Onsager-type theory for binary hard rod mixtures qualitatively describes the observed phase behavior.

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Liquid crystal formation in DNA fragment solutions

et al. 1998

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The critical volume fractions pertaining to the formation of DNA liquid crystals were obtained from polarization microscopy, 31 P-nmr, and phase separation experiments. The DNA length (approximately one to two times the persistence length 50 nm), ionic strength, and counterion variety dependencies are reported. The cholesteric-isotropic transition is interpreted in terms of the coexistence equations, which are derived from the solution free energy including orientational entropy and excluded volume effects. With the wormlike chain as reference system, the electrostatic contribution to the free energy is evaluated as a thermodynamic perturbation in the second virial approximation with a Debye-Hu ¨ckel potential of mean force. The hard core contribution has been evaluated with scaled particle theory and/or a simple generalization of the Carnahan-Starling equation of state for hard spheres. For sufficiently high ionic strengths, the agreement is almost quantitative. At lower amounts of added salt deviations are observed, which are tentatively attributed to counterion screening effects. The contour length dependence agrees with a DNA persistence length 50 nm.

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Concentrated solutions of liquid-crystalline polymers

Cited by 154 publications

References 137 publications

Synthesis and structure determination of helical polymers

Synthesis and structure determination of helical polymers

Nematic Phase Transitions in Mixtures of Thin and Thick Colloidal Rods

Liquid crystal formation in DNA fragment solutions

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