Molecular Structure and Rubberlike Elasticity. II. The Stereochemistry of Chain Polymers

1942 ◽  
Vol 15 (4) ◽  
pp. 731-741
Author(s):  
C. W. Bunn
Keyword(s):  
Molecular Geometry ◽  
Sufficient Evidence ◽  
Zigzag Chain ◽  
X Ray Diffraction ◽  
Molecular Physics ◽  
Chain Molecules ◽  
X Ray ◽  
Gutta Percha ◽  
Extended Plane ◽  
Long Chain

Abstract In Part I of this work, the determination of the crystal structures of three long-chain polymers by interpretation of x-ray diffraction photographs was described. In all three crystals—β-gutta-percha, rubber and polychloroprene—themolecules have nonplanar zigzag chain forms and are asymmetric. It is now necessary to consider the bearing of the new knowledge of molecular geometry on the possibility of understanding rubber like properties in terms of molecular physics. It is widely believed that the flexibility, softness and other characteristic properties of rubberlike substances are in some way due to the flexibility of the molecules themselves. Long-chain molecules owe their potential flexibility to the swivelling of the chain units around the single bonds as axes, and it is therefore necessary to consider which bond positions are the most stable and what hindrances there are to rotation away from these positions. The present paper deals chiefly with the question of the most stable bond positions. The enquiry has interest, not only in relation to the problem of the origin of rubberlike properties, but also because it opens the way to a systematic consideration of chain types. There is already evidence that in many crystalline long-chain polymers, such as rubber hydrochloride, polyisobutylene, and some of the polyesters, the chains have not the fully extended plane zigzag form of polyethylene, but somewhat shortened (necessarily nonplanar) forms. It should be possible to discover what these forms are by interpretation of x-ray diffraction photographs, but the difficulties are in some cases formidable; some assistance in the form of guiding principles for the construction of possible chain types is desirable. It is the purpose of this paper to show that sufficient evidence already exists to suggest a general principle regulating bond positions in aliphatic molecules containing sequences of singly linked atoms. It will be called the principle of staggered bonds. In the three molecules whose structures were determined in Part I, every fourth chain bond is a double bond; the question of bond positions is less simple for such molecules than it is for those in which all the bonds are single. The latter will therefore be considered first.

An X-Ray Investigation of Crystallinity in Rubber

1939 ◽  
Vol 12 (4) ◽  
pp. 706-718
Author(s):  
S. D. Gehman ◽  
J. E. Field
Keyword(s):  
Crystalline Structure ◽  
Polymeric Materials ◽  
The Other ◽  
X Ray Diffraction ◽  
Random Orientation ◽  
Chain Molecules ◽  
Micellar Structure ◽  
X Ray ◽  
Recent Developments ◽  
Long Chain

Abstract The crystalline structure which rubber exhibits under certain circumstances has come to be regarded as associated with a secondary or micellar structure of long chain molecules. The exact mechanism by which the localized ordered regions appear is a speculative subject in recent developments of the micellar theory of long chain polymeric materials. The views of various workers on this subject have been summarized by other authors. The crystalline structure of rubber displays varying degrees and types of orientation of the crystal units, depending on the conditions under which crystallization occurs. The amorphous x-ray diffraction pattern of unstretched rubber is shown in Figure 1, the unoriented crystalline diagram for frozen rubber in Figure 2. When crystallization is induced by stretching, the crystallites are aligned along the axis of stretching, giving the fiber diagrams of Figures 3 and 4. In this case there is random orientation of the other two axes of the crystallites. “Higher orientation,” in which all three axes of the crystallites are aligned, gives the diagram of Figure 15 and can be secured with suitable dimensions of the stretched piece.

Observations on the X-Ray Structure of Rubber and the Size and Shape of Rubber Crystallites

1944 ◽  
Vol 17 (3) ◽  
pp. 640-652
Author(s):  
S. D. Gehman ◽  
J. E. Field
Keyword(s):  
Molecular Structure ◽  
Physical Properties ◽  
X Ray Diffraction ◽  
Ray Method ◽  
Chain Molecules ◽  
X Ray ◽  
Rubberlike Material ◽  
Molecular Forces ◽  
Ray Patterns ◽  
Long Chain

Abstract In former times, we used to be painfully aware of the shortcomings and elastic imperfections of Hevea rubber. With its disappearance, we have come to think of it as having an ideal balance in physical properties for a rubberlike material which it has been difficult to approach with synthetic polymers. for this reason, it is still important to investigate the molecular structure of Hevea rubber and to try to understand the characteristics of this structure which are responsible for its physical properties. X-Ray diffraction methods can be applied to the problem of the molecular structure of Hevea rubber and a few synthetic rubbers, such as Butyl rubber and Neoprene, because crystallization occurs upon stretching. A detailed description of the x-ray diffraction results with rubber is available in a review article and need not be repeated here. It should be pointed out that the story obtained from the x-ray structure is not complete because there are important aspects of the structure which are not revealed by this means. It is not possible to measure directly the length of the chain molecules. The nature of the amorphous phase, such as the system of cross-linking of the long chain molecules on vulcanization, does not become evident in x-ray patterns. The physical properties of Hevea rubber must depend on a delicate balance of primary and secondary valence forces. The x-ray method does not permit any direct measurement of these forces but merely shows the geometrical arrangement which results from the molecular forces. Even with these limitations, much valuable information can be secured on the nature of the molecular rearrangements which occur upon stretching. Deductions can be drawn from the x-ray diffraction results regarding the form and spatial relationships of the long chain polymeric molecules and the manner in which they interact under stress. Correlations can then be looked for between the crystallization and the physical properties.

X-Ray Diffraction Patterns of Crystalline Sol Rubber Prepared from Ethereal Solution

1939 ◽  
Vol 12 (3) ◽  
pp. 482-484
Author(s):  
George L. Clark ◽  
Siegfried T. Gross ◽  
W. Harold Smith
Keyword(s):  
Sol Gel ◽  
Crystalline Material ◽  
X Rays ◽  
X Ray Diffraction ◽  
Experimental Procedure ◽  
Chain Molecules ◽  
X Ray ◽  
Measurement And Analysis ◽  
Diffraction Patterns ◽  
Long Chain

Abstract In a previous publication there was reproduced an x-ray diffraction pattern of crystals obtained from a solution, cooled to temperatures between −40° and −50° C, of an ether-gel fraction of rubber from Hevea brasiliensis. Measurements of three strong interferences indicated that the crystals were similar to those of stretched gel rubber and of frozen sol, gel and total rubber. Although many attempts were made at that time, unsatisfactory diffraction patterns were obtained with crystalline ether-sol rubber. The interferences were faint and not suitable for accurate measurement and analysis. Since the crystalline material is bulky and some specimens are more compact than others, it seemed possible that the average number of cell diameters was too small to permit sharp definition, and that more material was required for the examination by x-rays. However, it is not certain that lack of definition was caused by insufficient crystalline rubber. The possibility that parts of the long-chain molecules become crystalline and that parts remain amorphous is not excluded, and might be its cause. Additional work with crystalline sol rubber, using a slightly different experimental procedure and more material than in earlier experiments, finally resulted in a satisfactory pattern.

A 2-D Zn(II) coordination polymer based on 4,5-imidazoledicarboxylate and bis(benzimidazole) ligands: synthesis, crystal structure and fluorescence properties

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Xinzhao Xia ◽  
Lixian Xia ◽  
Geng Zhang ◽  
Yuxuan Jiang ◽  
Fugang Sun ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Coordination Polymer ◽  
Zigzag Chain ◽  
Supramolecular Framework ◽  
X Ray Diffraction ◽  
Hydrothermal Conditions ◽  
Hydrogen Bond Interaction ◽  
X Ray ◽  
New Type ◽  
Solid State Fluorescence

Abstract In this work, a new type of zinc(II) coordination polymer {[Zn(HIDC)(BBM)0.5]·H2O} n (Zn-CP) was synthesized using 4,5-imidazoledicarboxylic acid (H3IDC) and 2,2-(1,4-butanediyl)bis-1,3-benzimidazole (BBM) under hydrothermal conditions. Its structure has been characterized by infrared spectroscopy, elemental analysis and single crystal X-ray diffraction analysis. The Zn(II) ion is linked by the HIDC2− ligand to form a zigzag chain by chelating and bridging, and then linked by BBM to form a layered network structure. Adjacent layers are further connected by hydrogen bond interaction to form a 3-D supramolecular framework. The solid-state fluorescence performance of Zn-CP shows that compared with free H3IDC ligand, its fluorescence intensity is significantly enhanced.

The Molecular Geometry of Diastereoisomeric Bis[α-(9-anthryl)ethyl] Ethers

1985 ◽  
Vol 38 (9) ◽  
pp. 1417 ◽  
Author(s):  
H Becker ◽  
VA Patrick ◽  
BW Skelton ◽  
AH White
Keyword(s):  
Single Crystal ◽  
Least Squares ◽  
Dihedral Angle ◽  
Molecular Geometry ◽  
Dihedral Angles ◽  
Methyl Groups ◽  
X Ray Diffraction ◽  
X Ray ◽  
Meso Form ◽  
Aromatic Systems

The crystal structures of racemic bis [α-(9-anthryl)] ether and its meso form have been determined by single-crystal X-ray diffraction methods at 295 K, being refined by least squares to residuals of 0.053 and 0.041 for 1868 and 3568 independent 'observed' reflections respectively. Crystals of the racemate are orthorhombic, Pcab, a 23.07(1), b 19.85(2), c 10.241(8) Ǻ, Z 8. Crystals of the meso form are triclinic, Pī , a 19.032(12), b 14.207(11), c 9.451(8) Ǻ, α 79.46(6), β 89.68(6), γ 68.97(5)°, Z 4. In the racemate , the dihedral angle between the methyl groups along the ether bonds is 12°, and the short axes of the anthracene moieties lie at an angle of about 120°. In the meso compound, for the two molecules the dihedral angles between the methyl groups along the ether bonds are 90 and 93°, the angle between the two anthracene moieties is 90°, and the interplanar angles between the partly overlapping aromatic systems are 46 and 43°.

The Epicuticle of an Arachnid, Palamneus swammerdami

1954 ◽  
Vol s3-95 (31) ◽  
pp. 371-381
Author(s):  
G. KRISHNAN
Keyword(s):  
Outer Membrane ◽  
Diffraction Pattern ◽  
Basal Layer ◽  
Thin Membrane ◽  
Basic Pattern ◽  
X Ray Diffraction ◽  
X Ray ◽  
Chemical Constitution ◽  
Long Chain

The epicuticle of Palamneus swammerdami in the unhardened condition is homogeneous. It stains uniformly red with Mallory. When hardened, it comprises an internal unstained region, giving evidence of --S--S-- bonding, and is bounded externally by a very thin membrane which stains blue with Mallory. The protein of the inner basal layer differs from its counterpart in the insect epicuticle in the absence of tyrosine, in the occurrence of cystine and cysteine, and in being resistant to the action of hot alkalis. Though apparently related to the keratin of vertebrates, it is not identical with it. The outer thin membrane is lipide in nature. X-ray diffraction studies show that the epicuticular protein is unique: it is unlike both arthropodin and the keratin of vertebrates. However, the outer membrane of the epicuticle yields a diffraction pattern indicating the presence of long-chain paraffins and is similar to the outer epicuticle of the blowfly larva. The chitin of the cuticle appears to be identical in pattern with that of insects. In spite of differences in structural and chemical constitution, the epicuticle of the scorpion shows a resemblance to the basic pattern of the insect epicuticle. The differences may be attributed to the absence of phenolic tanning and the occurrence of --S--S-- bonding. The possible role of the purines present in the cuticle of the scorpion is discussed in relation to --S--S-- bonding.

The Structure of Polyisoprenes. II. The Structure of β-Gutta-Percha

1945 ◽  
Vol 18 (2) ◽  
pp. 280-283
Author(s):  
G. A. Jeffrey
Keyword(s):  
Molecular Structure ◽  
Double Bond ◽  
Diffraction Data ◽  
X Ray Diffraction ◽  
Interatomic Distances ◽  
Methyl Group ◽  
X Ray ◽  
Gutta Percha ◽  
Qualitative Estimate

Abstract The x-ray diffraction data at present available from β-gutta-percha are shown to be insufficient to distinguish fine details of molecular structure. Since a qualitative estimate of the intensities on the fibre diagram can be adequately satisfied by a model having normal interatomic distances and valency angles, no evidence exists for the improbable distortion of the methyl group out of the plane of the double bond previously ascribed to the molecule.

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