The Diamagnetic Anisotropy of Natural and Synthetic Rubbers

1952 ◽  
Vol 25 (4) ◽  
pp. 759-766
Author(s):  
Elizabeth Weir Toor ◽  
P. W. Selwood
Keyword(s):  
Magnetic Anisotropy ◽  
Natural Rubber ◽  
Degree Of Crystallinity ◽  
Cross Linking ◽  
Double Bonds ◽  
Chain Molecules ◽  
Diamagnetic Anisotropy ◽  
Actual Degree ◽  
Long Chain ◽  
Natural And Synthetic

Abstract The change in anisotropy with elongation has been found for natural rubber and for several synthetic rubbers. Unsaturated rubbers have a large principal susceptibility perpendicular to the direction of stretching, because of the presence of olefinic double bonds. The differences between natural rubber and polybutadiene are attributed to the presence of unsaturated side-groups caused by 1,2-addition in polybutadiene. Probably the magnetic anisotropy of these rubbers depends, not on the actual degree of crystallinity of the rubbers, but on the ability of the long-chain molecules to align themselves parallel to the direction of stretching. Therefore the changes in anisotropy with stretching are large when there is no cross-linking, and small when cross-linking occurs to any large extent. Saturated rubbers have an anisotropy opposite in sign to that of unsaturated rubbers. This must be caused by the broadening of electronic orbits perpendicular to the direction of stretching. Apparently methyl side-groups cause such a broadening of electronic orbits in polyisobutylenes, an effect much greater than the similar effect in polyethylene.

Radical Mechanisms in Saturated and Olefinic Systems. II. Disubstitutive Carbon-Carbon Cross-Linking by Tertiary Alkoxy Radicals in Isoprenic Olefins and Rubber

1951 ◽  
Vol 24 (4) ◽  
pp. 777-786
Author(s):  
E. H. Farmer ◽  
C. G. Moore
Keyword(s):  
Natural Rubber ◽  
Cross Linking ◽  
Chain Molecules ◽  
Alkoxy Radicals ◽  
Full Extent ◽  
Carbon Chains ◽  
Butyl Peroxide ◽  
High Degree ◽  
Vulcanization Process

Abstract The high degree of dehydrogenation effected by tert.-butoxy radicals at the α-methylenic groups of olefins enables these radicals to be used for the carbon-to-carbon cross-linking of unsaturated carbon chains, and especially of the polyisoprenic chains of natural rubber. Such cross-linking amounts to a vulcanization process in which the connecting links between chain molecules are just C—C bonds, which may be expected to have appropriate attributes. An examination has first been made of the cross-linking produced by tert.- butoxy radicals (from di-tert.-butyl peroxide) at 140° between the short iso-prenic chains in 1-methylcyclohexene, 4-methylhept-3-ene, 2,6-dimethylocta-2, 6-diene, and digeranyl. Cross-linking proceeds efficiently in each case, and the points of union in these isoprene units which become directly joined are not confined to original α-methylenic carbon atoms. Where the reagent radicals are in considerable deficit, e.g., one per two or three of the isoprene units present, those olefin molecules which are attacked become linked together mostly by single unions to form aggregates containing two, three or four molecules; but in the tetraisoprenic olefins the extent to which more than one union is formed between some of the directly linked molecules becomes appreciable. In natural rubber, cross-linking occurs smoothly and to nearly the full extent corresponding to the (in practice restricted) proportion of peroxidic reagent employed. Good vulcanizates can be so obtained in which the tensile stength is found to increase towards a maximum and then to decline rapidly as the degree of cross-linking steadily increases. Thus to obtain vulcanizates of the optimum physical characteristics, the degree of cross-linking must be suitably chosen. The role of the peroxidic reagent is almost entirely non-additive and non-degradative.

Mineral Sulfide as Index of Disulfide Cross-Bonding

1947 ◽  
Vol 20 (3) ◽  
pp. 649-663 ◽  
Author(s):  
C. M. Hull ◽  
S. R. Olsen ◽  
Wesley G. France
Keyword(s):  
Natural Rubber ◽  
Cross Linking ◽  
Diallyl Disulfide ◽  
Double Bonds ◽  
Metal Soap ◽  
Sulfide Production ◽  
Sulfur Vulcanization

Abstract 1. The mechanism proposed by Armstrong, Little, and Doak to explain sulfur vulcanization in the presence of metal soap was investigated in polyprene and simpler systems from the viewpoint of the inorganic sulfide produced and, in the case of polyprenes, of the accompanying modulus. 2. Dodecanethiol was found to react with sulfur and zinc soap to produce inorganic sulfide equivalent to the oxidation of 80 to 100 per cent of the thiol to disulfide ; with excess thiol substantially quantitative conversion of sulfur or of zinc soap to inorganic sulfide can be obtained. 3. Several simple olefins were found to react readily with sulfur and zinc soap under vulcanizing conditions. The reaction is promoted by M.B.T. On the basis of the mechanism assumed, the inorganic sulfide formed is sufficient to indicate extensive conversion of the olefin to a substituted diallyl disulfide. 4. Assuming the validity of the proposed mechanism, inorganic sulfide production indicates substantial disulfide cross-linking between α-carbon atoms in conventional cures with natural rubber, and appreciable, though relatively less, cross-bonding of this type in the case of GR-S. The smaller extent of this type of cross-linking with GR-S is believed to result from greater tendency on the part of this elastomer to add the intermediate mercapto compound to double bonds, as proposed in the first paper of this series.

Natural and Synthetic Rubber. I. Products of the Destructive Distillation of Natural Rubber

1929 ◽  
Vol 2 (3) ◽  
pp. 441-451 ◽  
Author(s):  
Thomas Midgley ◽  
Albert L. Henne
Keyword(s):  
Experimental Data ◽  
Natural Rubber ◽  
Atmospheric Pressure ◽  
Experimental Results ◽  
Double Bonds ◽  
Synthetic Rubber ◽  
Single Bonds ◽  
Natural And Synthetic

Abstract Two hundred pounds of pale crepe rubber have been destructively-distilled at atmospheric pressure. The distillate was fractionated and its components identified from C5 to C10, as shown in the table. Assuming that the Staudinger formula is correct, that the single bonds furthest from the double bonds are the weaker spots and that the formation of six-carbon rings is favored, it has been shown that nearly all of the compounds actually isolated could be predicted. The experimental results, together with forthcoming experimental data, are expected to be used to throw light upon the formula of the rubber molecule.

The Rubber-like Behavior of an Artificial Substance (Oppanol) when Irradiated with X-rays

1938 ◽  
Vol 11 (4) ◽  
pp. 687-688
Author(s):  
R. Brill ◽  
F. Halle
Keyword(s):  
Natural Rubber ◽  
Normal State ◽  
X Rays ◽  
Organic Substances ◽  
Chain Molecules ◽  
X Ray ◽  
Natural Substances ◽  
Amorphous Sulfur ◽  
Definite Temperature ◽  
Long Chain

Abstract As is known, natural rubber has the property of giving, when stretched, an x-ray fiber diagram, whereas in a normal state the same rubber is amorphous. Numerous other natural substances such as hair and tendon, and artificial substances such as polychloroprene, behave in the same way. However, this effect is not confined to purely organic substances, and it is to be found, for example, in the case of so-called amorphous sulfur and polyphosphornitryl chloride (PNCl2)x. All these substances have the property in common with one another of exhibiting a rubber-like elasticity within a definite temperature range, and of being composed of long-chain molecules.

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.

Properties of Some Synthetic Rubbers

1943 ◽  
Vol 16 (4) ◽  
pp. 857-862
Author(s):  
L. B. Sebrell ◽  
R. P. Dinsmore
Keyword(s):  
Molecular Structure ◽  
Natural Rubber ◽  
Point Of View ◽  
General Point ◽  
Chain Molecules ◽  
X Ray ◽  
Synthetic Rubber ◽  
The Difference ◽  
Diffraction Patterns ◽  
Long Chain

Abstract X-RAY STRUCTURE OF SYNTHETIC RUBBER In presenting a series of x-ray diagrams of various types of synthetic rubber in comparison with natural rubber, in both the stretched and the unstretched condition, it is our purpose to bring out the fact that the molecular structure of synthetic rubbers is entirely different from that of natural rubber. It is proposed also to review briefly the theories which have been advanced, based on the x-ray analysis of rubber, to account for the elasticity of natural rubber, and to advance the possible reason for the difference shown by the x-ray diagrams of synthetic rubber. At the present time, from the most general point of view, the molecular structure of a rubberlike material is envisaged as a sort of brush-heap structure of entangled long chain molecules. x-Ray diffraction patterns show that, for some rubberlike materials, notable regularities of structure sometimes occur in the tangle of long-chain molecules. It is now realized that these regularities are not essential for rubberlike behavior. Nevertheless their observation and study is important because they afford a unique opportunity for studying the molecular structure of the chains and the molecular rearrangements which occur with the application of stress.

Natural and Synthetic Rubber. VI. the Pyrolysis of Natural Rubber in the Presence of Metallic Oxides

1931 ◽  
Vol 4 (1) ◽  
pp. 98-99
Author(s):  
Thomas Midgley ◽  
Albert L. Henne
Keyword(s):  
Zinc Oxide ◽  
Natural Rubber ◽  
Magnesium Oxide ◽  
Double Bonds ◽  
Decomposition Products ◽  
Metallic Oxides ◽  
Synthetic Rubber ◽  
Natural And Synthetic

Abstract Pale crepe rubber pyrolyzed in the presence of zinc oxide or magnesium oxide gives the same decomposition products as in the absence of the oxides, but in different proportions. This modification is attributed to an action of the oxides upon the double bonds of the rubber molecule.

Molecular Requirements for Synthetic Rubbers

1945 ◽  
Vol 18 (3) ◽  
pp. 632-636 ◽  
Author(s):  
W. O. Baker
Keyword(s):  
Natural Rubber ◽  
Small Groups ◽  
Close Packing ◽  
Chain Molecules ◽  
Lateral Forces ◽  
Chain Compounds ◽  
Simple Chain ◽  
A Chain ◽  
Model Chain ◽  
Long Chain

Abstract Rubbery substances consist basically of long chains of atoms to which other atoms may be attached in small groups that occur repeatedly, and often regularly, like the links along a chain. There are hundreds of atoms in one of these “macro” molecules. It is the particular arrangement and the active forces between these molecules that are responsible for the elastic properties of many substances. The structure of the molecules of most synthetic rubbers as well as that of natural rubber is so complex, however, that efforts to determine, by direct study of the commercial products, what produces their rubbery characteristics have yielded results that are difficult to interpret. Progress in solving the puzzle has recently been made by starting with simple chain compounds and forming from them, by known chemical modifications, substances which have some of the properties that are found in natural rubber. Studies of these “model” chain compounds indicate that the long-chain molecules of rubbery substances must have forces between atomic groups which are small enough to permit twisting and kinking of the chains. There must also be lateral forces to hold adjacent molecules together, like a bundle of sticks, especially when the substance is stretched. Moreover, the molecules must have side groups to avoid the close packing, when unstretched, that is characteristic of crystals.

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