Recent Advances in the Physics and Chemistry of Rubber. IV. Crystallization in Rubbers

1945 ◽  
Vol 18 (4) ◽  
pp. 724-730
Author(s):  
L. R. G. Treloar
Keyword(s):  
Physical Properties ◽  
Crystalline Phase ◽  
Geometrical Shape ◽  
Chain Molecules ◽  
Recent Advances ◽  
Structural Regularity ◽  
Adequate Representation ◽  
The Individual ◽  
Simple Picture ◽  
Long Chain

Abstract In dealing with elasticity and with swelling, we have thus far considered rubber to be composed of a loose network of randomly-kinked long-chain molecules. This simple picture does not fully represent the structure of rubber under all conditions, and gives no explanation of many of the remarkable physical properties of raw rubber. For a more adequate representation we are forced to include the effects of crystallization. In this Part we shall examine some of these effects, and see what light they throw on the mechanism of the process of crystallization and on the structure of rubber generally. At the outset we may find some difficulty in accepting the theory that rubber may contain a crystalline phase. This is because we are accustomed to think of a crystal as possessing a precise geometrical shape. We cannot identify such geometrical forms in rubber. But, on consideration, we see that the essential attribute of a crystal is the internal regularity of the spacing of its constituent atoms. The external geometrical regularity, where it exists, is derived from this more fundamental internal structural regularity. It is frequently found, however, that the internal regularity is not accompanied by external regularity. This is true, for example, of the metals, which are invariably crystalline. The absence of external regularity is due to the small size of the individual crystallites. The same considerations apply to rubbers.

scholarly journals The structure of polychloroprene

1942 ◽  
Vol 180 (980) ◽  
pp. 100-107 ◽  
Keyword(s):  
Physical Properties ◽  
Crystalline Structure ◽  
Light Treatment ◽  
Unit Cell ◽  
Cross Linking ◽  
Chain Molecules ◽  
X Ray ◽  
Before And After ◽  
Ray Methods ◽  
Long Chain

Specimens of polychloroprene before and after light treatment have been examined by X -ray methods. There is no change in the crystalline structure, although there are differences in the physical properties ascribed to cross-linking of the long-chain molecules. The unit cell is possibly ortho­rhombic: a = 8·90 A , b = 4·70 A, c = 12·21 A, and contains four chloroprene (C 4 H 5 Cl) units.

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.

Recent Advances in the Total Synthesis of Clavaminols

Synthesis ◽  
2018 ◽  
Vol 50 (23) ◽  
pp. 4569-4576
Author(s):  
Tian Jin ◽  
Lu Zhao ◽  
Zhe-Bin Zheng ◽  
Xiao Liu ◽  
Liang Sun ◽  
...  
Keyword(s):  
Total Synthesis ◽  
Research Groups ◽  
Total Syntheses ◽  
New Class ◽  
Recent Advances ◽  
Molecular Architectures ◽  
Synthetic Approaches ◽  
Long Chain

Clavaminols are a new class of long-chain 2-amino-3-­alkanols that mostly contain 2R,3S-configurations. Owing to their interesting molecular architectures and promising activities, they have ­become popular targets for synthetic organic chemists. In this review, we highlight 12 total syntheses of clavaminols from different research groups during the period 2009 to 2018.1 Introduction2 Synthetic Approaches toward Clavaminols2.1 Total Synthesis by Chemla and Colleagues (2009)2.2 Total Synthesis by Greck and Colleagues (2010)2.3 Total Synthesis by Sutherland and Zaed (2011)2.4 Total Synthesis by Huang and Colleagues (2011)2.5 Total Synthesis by Kotora and Colleagues (2012)2.6 Total Synthesis by Kumar and Colleagues (2013)2.7 Total Synthesis by Prabhavathi Devi and Colleagues (2013 and 2016)2.8 Total Synthesis by Sarabia and Colleagues (2014)2.9 Total Synthesis by Mohapatra and Colleagues (2016)2.10 Total Synthesis by Lu and Colleagues (2016)2.11 Total Synthesis by Jin and Colleagues (2017)2.12 Total Synthesis by Kumar Pandey and Colleagues (2018)3 Conclusion

Conformational transitions of long chain molecules in frozen solutions

1989 ◽  
Vol 91 (11) ◽  
pp. 7296-7299 ◽  
Author(s):  
R. Hirschmann ◽  
J. Friedrich ◽  
E. Daltrozzo
Keyword(s):  
Conformational Transitions ◽  
Chain Molecules ◽  
Frozen Solutions ◽  
Long Chain

Theory of Depolymerization of Long Chain Molecules

1940 ◽  
Vol 8 (9) ◽  
pp. 721-726 ◽  
Author(s):  
Elliott W. Montroll ◽  
Robert Simha
Keyword(s):  
Chain Molecules ◽  
Long Chain
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