Helix-Inversion Equilibrium of Isotactic Chloral Oligomers in Solution

Ute, Koichi; Hirose, Katsuo; Kashimoto, Hiroaki; Nakayama, Hiroko; Hatäda, Koichi; Vogl, Otto

doi:10.1295/polymj.25.1175

Cited by 35 publications

(47 citation statements)

References 25 publications

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“…The (-)-pentamer with the (R,R,R,R,R) main-chain configuration was unambiguously determined to be a right-handed 4/1 helical structure on the basis of an X-ray crystallographic analysis. 45 Isotactic and enantiomerically pure uniform oligomers similar in structure to 13, but bearing identical end groups (14), have also been isolated. The oligomers have a meso structure, but are chiral, because of their helicity.…”

Section: Helical Structure Determination By Single-crystal X-ray Analmentioning

confidence: 98%

“…18,44 However, the polychloral is insoluble in solvents, and further investigations in solutions were difficult. Ute et al 45 prepared and isolated a series of isotactic and enantiomerically pure uniform oligomers bearing different end groups (13) by size-exclusion chromatography (SEC) from oligomerization products, which were further resolved into enantiomers by chiral high-performance liquid chromatography. The (-)-pentamer with the (R,R,R,R,R) main-chain configuration was unambiguously determined to be a right-handed 4/1 helical structure on the basis of an X-ray crystallographic analysis.…”

Section: Helical Structure Determination By Single-crystal X-ray Analmentioning

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 By Single-crystal X-ray Analmentioning

confidence: 98%

Section: Helical Structure Determination By Single-crystal X-ray Analmentioning

confidence: 99%

Synthesis and structure determination of helical polymers

Yashima

2010

Polym J

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“…From our investigations of the optical rotations of chloral oligomers we have learned that they have rotations of only about 60 degrees. We have consequently concluded that the high optical rotation of chloral polymers is a special property of the solid state of the optically active polychloral films [23]. The ester could be reduced to the aldehyde.…”

Section: Polymers Of the Chiral Fluorochlorobromoacetaldehydementioning

confidence: 82%

“…One additional but important identification was to resolve the individual oligomers into the optical antipodes (R,R,...,R and S,S,...,S isomers) by a chiral HPLC technique [23].…”

Section: It Was Alsomentioning

confidence: 99%

Stereoregular and conformationally regular oligomers and polymers

Vogl¹,

Simonsick

Bartus³

et al. 1994

Macromolecular Symposia

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SUMMARYConfigurationally and conformationally regular polymers can now be synthesized based on sterically restrictive considerations.Trihaloacetaldehyde polymerization provided a fertile field for the investigation of the factors for such polymer formations.The convenient ceiling temperature of trihaloacetaldehyde polymerizations allowed the study of the genesis of these polymerizations.Oligomers were prepared by alkoxide initiation, followed by the establishment of the oligomer alkoxide equilibrium and end-capping.Stereoregularity and conformational regularity were observed in trichloroacetaldehyde (chloral) and tribromoacetaldehyde (bromal) polymerizations.This result was confirmed by solid state magic angle spinning NMR investigations of polychloral, of polybromal as well as of a copolymer of chloral and bromal. Solid state NMR techniques allowed also to investigate copolymers of chloral and aromatic isocyanates.Quantification of the solid state investigation suggests the possibility of a molecular weight estimation of chloral and other insoluble trihaloacetaldehyde polymers by end-group analysis. STEREOREGULAR AND CONFORMATIONALLY REGULAR POLYMERSFor some time we have been engaged in the study of stereoregular polymers [l], particularly the preparation of stereoregular and conformationally specific polymers of trihaloacetaldehydes [2,3].

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“…[45] Uniform chloral oligomers from dimer to nonamer were isolated by SEC from oligomer mixtures prepared with tC 4 H 9 OLi. [46][47][48][49][50][51][52][53][54][55] …”

Section: Uniform Polymers From Addition Polymerizationsmentioning

confidence: 99%

Synthetic Uniform Polymers and Their Use for Understanding Fundamental Problems in Polymer Chemistry

Hatäda

Kitayama

Ute

et al. 2004

Macromol. Rapid Commun.

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Summary: A uniform polymer is a polymer composed of molecules that are uniform with respect to molecular weight and constitution. Besides natural uniform polymers such as nucleic acids and polypeptide, synthetic uniform polymers have been obtained by a variety of approaches. In particular, a combination of living polymerization and supercritical fluid chromatography (SFC) separation is one of the promising ways for the preparation of uniform polymers. End‐functionalized uniform polymers enabled us to prepare uniform polymer architectures such as block, graft, comb, and star polymers. Their use for understanding the fundamental problems in polymer chemistry is discussed; topics include crystallization of polymers, chain conformation in solution, and association of stereoregular polymers in solution.

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Helix-Inversion Equilibrium of Isotactic Chloral Oligomers in Solution

Cited by 35 publications

References 25 publications

Synthesis and structure determination of helical polymers

Synthesis and structure determination of helical polymers

Stereoregular and conformationally regular oligomers and polymers

Synthetic Uniform Polymers and Their Use for Understanding Fundamental Problems in Polymer Chemistry

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