Structural Refinement and Extraction of Hydrogen Atomic Positions in Polyoxymethylene Crystal Based on the First Successful Measurements of 2-Dimensional High-Energy Synchrotron X-ray Diffraction and Wide-Angle Neutron Diffraction Patterns of Hydrogenated and Deuterated Species

Tashiro, Kohji; Hanesaka, Makoto; Ohhara, Takashi; Kitano, Toshiaki; Nishu, Takashi; Kurihara, Kazuo; Tamada, Taro; Kuroki, Ryota; Fujiwara, Satoru; Tanaka, Ichiro; Nakabayashi, Nobuo

doi:10.1295/polymj.pj2007076

Cited by 32 publications

(28 citation statements)

References 24 publications

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“…c % 5571,0 pm = 29 Â 192,1 pm, und die Zahlenwerte von 9/5 = 1,80 und 29/16 = 1,8125 Wiederholungseinheiten pro Windung liegen nahe beieinander. Einige wenige sehr schwache Reflexe sprechen in diesem Fall eher fü r 29/16 (Tashiro et al, 2007).…”

Section: Experimentelle Einschränkungenunclassified

Die Symmetrie von Spiralketten

Müller

2017

Acta Crystallogr B Struct Sci Cryst Eng Mater

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In crystals, polymeric chain molecules often adopt helical structures. Neglecting small distortions possibly caused by an anisotropic environment within the crystal, the symmetry of the single helix can be described by a rod group, which has translational symmetry in one dimension. The rod groups have Hermann-Mauguin symbols similar to space groups, beginning with a script style \scr p followed by a screw-axis symbol; the order of the screw axis can adopt any value. In a crystal, the rod-site symmetry, the so-called penetration rod group, must be a common crystallographic rod subgroup of the molecular rod group and the space group. Instructions are given for the derivation of the rod subgroups in question for a molecular helical rod group of any order. In polymer chemistry, a helix is designated by a (chemical) symbol like 7/2, which means 7 repeating units in 2 coil turns of covalent bonds per translational period. The corresponding Hermann-Mauguin screw-axis symbol is easily derived with a simple formula from this chemical symbol; for a 7/2 helix it is 7 or 7, depending on chirality. However, it is not possible to deduce the chemical symbol from the Hermann-Mauguin symbol, because it depends on where the covalent bonds are assumed to exist. Covalent bonds are irrelevant for symmetry considerations; a symmetry symbol does not depend on them. A chemically right-handed helix can have a left-handed screw axis. The derivation of the Hermann-Mauguin symbol of a multiple helix is not that easy, as it depends on the mutual position of the interlocked helices; conversion formulae for simpler cases are presented. Instead of covalent bonds, other kinds of linking can serve to define the chemical helix, for example, edge- or face-sharing coordination polyhedra.

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Section: Experimentelle Einschränkungenunclassified

Die Symmetrie von Spiralketten

Müller

2017

Acta Crystallogr B Struct Sci Cryst Eng Mater

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“…Th e crystal structure of POM has been studied by using infrared spectroscopy, X-ray, and electron diff raction [4], and refi ned by 2-dimensional X-Ray and neutron diff raction [3]. As reported above, POM shows two polymorphic forms with an orthorhombic and a hexagonal unit cell structure respectively.…”

Section: Crystal Structure Determinationmentioning

confidence: 99%

“…Although in the hexagonal structure, chains have been mainly supposed to be arranged in a 9/5 helix [10,27], some recent evidences support the non-uniform 29/16 helical model as the most plausible chain conformation of POM crystals [3]. In both the models, under the assumption of uniform helix, the number of monomeric units per turn is about 1.8.…”

Section: Rowsmentioning

confidence: 99%

“…However, the high degree of crystallinity makes POM diffi cult to process and, moreover, under rapid conditions signifi cant shrinkage and void formation arise due to the diff erent densities and thermal expansion coeffi cients between the amorphous and crystalline phases [3]. Shrinkage of polymers is undesirable when high size precision is required, since it aff ects the fi nal dimensions of industrial goods, whereas the presence of microvoids lowers the mechanical performance of materials and their strength [4].…”

Section: Introductionmentioning

confidence: 99%

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Structure and Morphology of Polyoxymethylene

Raimo¹

2014

Polyoxymethylene Handbook

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Polyoxymethylene (POM), its blends and composites, show high mechanical strength, excellent abrasion and fatigue resistances, lubricating properties and moldability, and therefore have a variety of applications. Properties of substances depend on the composition, crystalline structure and, particularly for polymer materials, on morphology generated by preparation or crystallization conditions. Th ese factors are thoroughly discussed in this chapter as they are very important to control the fi nal properties of materials. Th e knowledge of a variety of atomic, molecular and supermolecular assemblies of materials, together with the mechanical performances and other chemico-physical properties herein described, allows the identifi cation and use of the most appropriate POM sample for a specifi c application. Th e eff ect of additives on the POM morphology and properties has also been analyzed, beyond orientation, perfection and size of crystals in neat POM.

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“…In the crystal structure of POM, the non-uniform (9/5) helical chains are packed in the trigonal unit cell of a¼4.47 Å and c¼17.39 Å . 23 It should be noted that, the crystal structure is more complicated, as described by Tashiro et al 24 in their analysis of synchrotron X-ray and neutron diffraction data. The morphological structure of the crystalline phase may be classified into two types as extreme cases, an extended-chain crystal (ECC) and a folded chain crystal (FCC) or lamellar crystal, depending on the crystallization condition as well as the thermal and mechanical histories.…”

Section: Introductionmentioning

confidence: 96%

Cocrystallization phenomenon of polyoxymethylene blend samples between the deuterated and hydrogenated species

Kongkhlang

Reddy

Kitano

et al. 2010

Polym J

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The phenomenon of cocrystallization between the deuterated (D) and hydrogenated (H) species of a series of polyoxymethylene blends with various H/D ratios has been established on the basis of the detailed analysis of thermal and infrared (IR) spectral data. The melting and crystallization temperatures were found to shift continuously toward a higher temperature with an increase in the D content. The IR spectra were found to change remarkably depending on the H/D blend content. Both the thermal and the IR spectral observations definitely indicated the cocrystallization between the H and D chains in the common crystallite. These continuous changes could be interpreted by assuming that the arrays of the H and D chains in crystal lattice are random. Polymer Journal ( Keywords: cocrystallization; deuterated species; DSC; infrared spectra; isotopic blend; polyoxymethylene INTRODUCTION Semicrystalline polymers show complex microstructures or higherorder structures that consist of crystalline and amorphous regions. Control of the higher-order structure may govern the physical properties of the polymers. A better understanding of the formation process is required in order to control the higher-order structure of the polymer and develop new materials with better properties. As the first step, the aggregation state of the molecular chains in the crystallized bulk sample must be determined at the molecular level. As the polymer solid is built up by the complicated aggregation of more or less entangled chains, it is difficult to trace the trajectory of a single particular chain in the bulk sample. The isotopic blend between the deuterated (D) and hydrogenated (H) species is considered one of the most useful methods for studying the behavior of a single chain in the aggregation state on the basis of the difference in the thermal and vibrational characters that are due to the difference in atomic mass. In some cases, the difference in the neutron scattering length is also utilized successfully to distinguish the D and H species. 14,17,18 In such cases of isotopic blends, the cocrystallization must be confirmed to take place between the H and D species in the crystalline lattice. For example, the blends between the H and D species of the various types of polyethylene have been comprehensively studied for clarification of the cocrystallization phenomenon between the H and D species. [1][2][3][4][8][9][10][11]14,[16][17][18][19] In the case of samples that are a blend of H high-density polyethylene and D high-density polyethylene, slow

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Structural Refinement and Extraction of Hydrogen Atomic Positions in Polyoxymethylene Crystal Based on the First Successful Measurements of 2-Dimensional High-Energy Synchrotron X-ray Diffraction and Wide-Angle Neutron Diffraction Patterns of Hydrogenated and Deuterated Species

Cited by 32 publications

References 24 publications

Die Symmetrie von Spiralketten

Die Symmetrie von Spiralketten

Structure and Morphology of Polyoxymethylene

Cocrystallization phenomenon of polyoxymethylene blend samples between the deuterated and hydrogenated species

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