Rubber. Part XIV. The Behavior of Rubber with Iodine Chloride and with Dithiocyanogen

1931 ◽  
Vol 4 (3) ◽  
pp. 399-403
Author(s):  
Rudolf Pummerer ◽  
Herman Stärk
Keyword(s):  
Terminal Group ◽  
Double Bonds ◽  
Excess Iodine ◽  
A Value ◽  
Iodine Chloride ◽  
Great Excess ◽  
Cold Ether ◽  
Rubber Part ◽  
Cold Acetone ◽  
Fraction I

Abstract 1. The Determination of the Iodine Number of Rubber The investigation of carotinoids has shown us that a large excess of iodine chloride must be employed if conjugated systems of double bonds are to be completely attacked. If, for example, with isoprene 150% of the calculated quantity of iodine chloride is used, then the reaction reaches after one day and after one week only 1.77 and 1.80 double bonds, respectively. 200% of iodine chloride must be used in order to obtain the correct number of double bonds. A still greater excess of iodine chloride does not then change the results any further. Such isoprene systems, which have added a halogen atom on every carbon atom in the chain, are obviously stable to substitution by iodine chloride. The frequently discussed question of whether in rubber a pair of conjugated double bonds is present as a terminal group, therefore a true isoprene system, has been proved by Pummerer and Mann by means of iodine chloride. At that time, however, the results did not apply to isoprene. For that reason it was necessary again to titrate the rubber with a great excess of iodine chloride. In this way it was shown that trustworthy results were obtained only by using 110–120% of iodine chloride (100% = 1 mol. of iodine chloride per C5H8 group), accordingly with an excess of from 10–20% iodine chloride. Within this range the results of the titration did not vary. Also only very few (often none at all) acids appeared with the titration, and these could be disregarded. On the contrary, if a greater excess of iodine chloride is used, the iodine numbers and acid values are essentially higher, which, as is well known, indicate substitution. Thus with 200% iodine chloride a value of 147 was obtained. The same phenomenon is true of gutta-percha. The earlier titrations of rubber were accidentally carried out within the favorable range of excess iodine chloride, so that the values for sol-rubber have undergone scarcely any correction. We have now carried out iodine chloride titrations with six fractions of crepe sol-rubber extracted with cold acetone, then fractionally dissolved in cold ether, and in this way we have found, as for sol-rubber, values for alkali-purified latex. They are very close to 100 (Fraction I: 100.1; II: 100.3; III: 99.9, IV: 99.6; V: 100.0; VI: 99.9). No difference in the titre was established by the various fractions.

Halogenation of Ethylene Propylene Diene Rubbers

1971 ◽  
Vol 44 (4) ◽  
pp. 1025-1042 ◽  
Author(s):  
R. T. Morrissey
Keyword(s):  
Natural Rubber ◽  
Double Bonds ◽  
Optimum Amount ◽  
Ethylene Propylene ◽  
Rubber Compounds ◽  
Rubber Part ◽  
Curing Agents ◽  
Diene Rubbers ◽  
Curing Systems

Abstract The ethylene propylene diene rubbers (EPDM) have been modified by halogenation. The reaction has been considered as one mainly of addition to the double bonds of the diene portion of the rubber. Dehydrohalogenation may occur to varying degrees, depending on the conditions of the reaction and the diene present in the rubber. Part of the halogen is believed to be in the allylic position. The halogenated EPDM may be vulcanized by sulfur as well as many of the curing agents used for other halogen-containing polymers. Both types of curing systems can function in the same compound. Therefore, the halogenated EPDM rubbers can be covulcanized with the highly unsaturated elastomers such as natural rubber, cis polybutadiene, and the SBR rubbers. The excellent properties, resistance to ozone, and flexing, of the halogenated EPDM can be imparted to these elastomers using standard curing systems. Also, the uncured tack of halogenated EPDM can be improved by increasing amounts of natural rubber. In addition, other advantages are adhesion of these blends to other rubber compounds and metal. It has been shown that the cure compatibility properties of the halogenated EPDM can be varied as the halogen is increased in the rubber. Evidence has been presented which shows there is an optimum amount of halogen necessary for the best properties in mixtures with other elastomers.

The cyclization of natural rubber

1963 ◽  
Vol 273 (1354) ◽  
pp. 345-359 ◽  
Keyword(s):  
Natural Rubber ◽  
Stannic Chloride ◽  
Double Bonds ◽  
Perbenzoic Acid ◽  
Infra Red ◽  
Iodine Chloride ◽  
Series Of Experiments ◽  
Average Size ◽  
Kinetics Of ◽  
Reaction In Solution

Several methods of measuring the unsaturation remaining in natural rubber after cyclization have been compared. Approximate agreem ent was obtained with the reagents, perbenzoic acid, phenyl iododichloride and ozone; iodine chloride gave high values. Perbenzoicacid is considered the most satisfactory of these reagents. The unsaturation in some cyclized rubber samples was found to be below 20% of that in the original rubber. This value is inconsistent with a cyclized rubber structure of single rings each involving two isoprene units and supports instead a polycyclic structure. This structure is also supported by some degradation experiments. Infra-red spectroscopy shows that the double bonds remaining after cyclization are not of the original trialkyl-substituted type. Use has been made of measurements of total unsaturation by means of perbenzoic acid and of trialkyl-substituted double bonds by infra-red spectrometry to investigate the kinetics of the cyclization reaction in solution and catalyzed by stannic chloride. All the results were accurately fitted by theoretical equations derived for a reaction proceeding in stepwise fashion along the rubber chains. The average size of the polycyclic structures formed during cyclization was found to be independent of both rubber and catalyst concentrations but to be markedly dependent on the temperature, varying in a series of experiments from approximately one and a half condensed rings at 110 °C to six rings at 60 °C. The rate of the reaction was first order in the rubber and second order in the catalyst.

Isoprene and Rubber. Part 23. Cryoscopic Measurements of Rubber Solutions

1931 ◽  
Vol 4 (2) ◽  
pp. 201-205
Author(s):  
H. Staudinger ◽  
H. F. Bondy
Keyword(s):  
Molecular Weight ◽  
Double Bonds ◽  
Chain Cleavage ◽  
Rubber Part

Abstract Pummerer, Andriessen, and Gündel published a work with this title which contains a number of remarks about the communication of Staudinger, Asano, Bondy, and Signer. The following discussion deals with this subject. 1. Molecular Weight Determinations of Rubber in Camphor according to East Determinations of the molecular weight of rubber in camphor cannot explain the constitution of rubber because, as has been explained before, when rubber is heated in melted camphor, at 170°-180°, a very pronounced decomposition of the rubber to semi-colloidal cleavage products takes place. The rubber molecule is very unstable as a consequence of the peculiar position of the double bonds in the chain; cleavage takes place with extraordinary ease, and attention has already been called to the fact that the cleavage of hexaphenylethane into triphenylmethyl, of dicyclopentadiene into cyclopentadiene, as well as the migration of the ally group, e. g., in phenylallyl ethers, the mobility of the substituents in allyl residues and finally the extremely easy depolymerization of rubber, all have one and the same cause: namely, that a substituent in the ally! group is very loosely combined. These facts, which are of such importance in the chemistry of rubber, should not be ignored as happens in most works on rubber. In order to study the decomposition, we carried out viscosity determinations. As the following experiments show, the viscosity of rubber is much less after melting in camphor than before. There occurred a very great decomposition at 170°, as was to be expected, and the relation t1/t2 which characterizes the decomposition is about 15. If pure rubber is decomposed in boiling tetralin the relation t1/t2 = 6.2. The decomposition in camphor is, therefore, surprisingly great, possibly because of the greater concentration of the dissolved rubber. The camphor solution used was 10 per cent, that of tetralin on the contrary was only 1 per cent.

Sulfur Bond in Vulcanizates Implications of Halogen Reactions

1947 ◽  
Vol 20 (3) ◽  
pp. 627-648
Author(s):  
S. R. Olsen ◽  
C. M. Hull ◽  
Wesley G. France
Keyword(s):  
Double Bond ◽  
Carbon Tetrachloride ◽  
Sulfur Atom ◽  
Side Reactions ◽  
Double Bonds ◽  
Vulcanized Rubber ◽  
Iodine Chloride ◽  
Allyl Sulfide ◽  
Sulfur Bond

Abstract 1. When iodine chloride is used for the determination of double bonds in sulfur-vulcanized rubber or GR-S, it undergoes side reactions induced by combined sulfur. 2. Bromine in carbon tetrachloride is believed to give a satisfactory measure of the double bonds in a rubber-sulfur vulcanizate dissolved in dichlorobenzene-chloroform mixture. 3. The relation of one double bond consumed per sulfur atom combined in the rubber-sulfur type vulcanizate was confirmed. 4. Organic accelerators (in the absence of metal activators) catalyze the combination of sulfur without altering the ratio of one double bond loss per sulfur atom combined. 5. The introduction of a metal oxide or soap, such as zinc, causes a different type of vulcanization, which results in less than one double bond consumed per sulfur atom combined. 6. The reactions of propyl sulfide, dodecyl sulfide, propyl disulfide, allyl sulfide, methallyl sulfide, and butylmethallyl sulfide with iodine chloride and with bromine, respectively, are described. 7. The behavior of rubber-sulfur vulcanizates resembles that of butylmethallyl sulfide in reactions with iodine chloride and bromine, respectively; this suggests an alkyl-allyl type sulfur bond. 8. The theory of vulcanization proposed by Armstrong, Little, and Doak, based on the α-methylenic concept of Farmer, is supported by the findings of this investigation.

The Influence of Structure on the Chemical Activity and Vulcanizability of Butadiene Polymers

1958 ◽  
Vol 31 (3) ◽  
pp. 569-580 ◽  
Author(s):  
B. A. Dogadkin ◽  
A. V. Dobromyslova ◽  
F. S. Tolstukhina ◽  
N. G. Samsonova
Keyword(s):  
Linear Function ◽  
Relative Content ◽  
Double Bonds ◽  
Initial Region ◽  
Linear Region ◽  
Kinetic Curves ◽  
Perbenzoic Acid ◽  
Ordinate Axis ◽  
Sulfur Addition ◽  
Iodine Chloride

Abstract 1. Differences between the chemical reactivities of 1,4- and 1,2-structures of butadiene are found in the reactions with perbenzoic acid, iodine chloride, and sulfur. 2. The interaction of perbenzoic acid with solutions of butadiene polymers is represented by kinetic curves with an initial region of a high rate, mainly corresponding to the reaction of the double bonds of 1,4-structure, and a final linear region of a low rate, characterizing the reaction of the double bonds in the vinyl side chains of 1,2-structure. By extrapolation of the linear region to the ordinate axis it is possible to determine the relative contents of the 1,4- (and hence of the 1,2-) structure in the polymer. 3. The kinetic curves for the interaction of the polymer solutions with iodine chloride are of analogous form. The initial region of the kinetic curve represents addition at the double bonds, while the linear region corresponds to the substitution reaction. By extrapolation of the linear region to the ordinate axis it is possible to determine the actual double bond content of the polymer. 4. The kinetic curves for iodine liberation are also of similar form ; here the linear region corresponds to the substitution reaction, and the initial region corresponds to the cyclization reaction. The amount of iodine liberated in this reaction is a linear function of the content of the 1,2-structure in the polymer. 5. Mainly the double bonds of the 1,4-structure react when sulfur interacts with the polymer solutions. The total rate of sulfur addition is a linear function of the content of the 1,4-structure. 6. The activation energy for sulfur addition increases with increasing relative content of the 1,2-structure in the polymer. 7. Formation of sulfur crosslinks in vulcanizates occurs mainly as the result of reactions in the 1,4 polymer structure. In consequence, the degree of crosslinking ΔE/ΔS is a linear function of the relative content of 1,4-structure in the polymer.

The Unsaturation of Butadiene Rubbers. I

1949 ◽  
Vol 22 (2) ◽  
pp. 287-298
Author(s):  
A. A. Vasil'ev
Keyword(s):  
Intramolecular Cyclization ◽  
Degree Of Saturation ◽  
Double Bonds ◽  
Iodine Chloride ◽  
Iodine Bromide

Abstract 1. The data on the unsaturation of butadiene rubbers previously obtained by using the method based on the reaction with iodine bromide have been checked and confirmed with the aid of the reactions with pyridine sulfate dibromide and with iodine chloride. 2. The influence of various factors on the unsaturation of butadiene rubbers has been checked, and the possibility of estimating changes in unsaturation with the aid of the reaction with iodine bromide has been established. 3. The present investigation shows that, during the reaction between butadiene rubbers and halogens, it is impossible to attain a degree of saturation exceeding 85–90 per cent of the theoretical values. This is apparently due to the existence of intramolecular cyclization, to the presence of intermolecular connecting bridges, and possibly to the presence of double bonds resistant to halogenation or of conjugated double bonds in the molecules of these rubbers. The reaction with halogens offers no possibility of confirming these suppositions experimentally.

Isoprene and Rubber. Part 30. Hydromethylrubber

1932 ◽  
Vol 5 (2) ◽  
pp. 141-145
Author(s):  
H. Staudinger ◽  
M. Brunner ◽  
E. Geiger
Keyword(s):  
Molecular Weight ◽  
High Pressure ◽  
Average Molecular Weight ◽  
Degree Of Polymerization ◽  
Methyl Groups ◽  
Butadiene Rubber ◽  
Double Bonds ◽  
Molecular Product ◽  
Unsaturated Rubber ◽  
Rubber Part

Abstract When rubber is reduced at 270° under high pressure, a hemi-colloidal hydrorubber is obtained, and it was proved by Geiger and Huber that the product has a higher molecular weight and is less cyclicized if a good catalyst is used in large quantity (for example, active nickel produced by the method of Kelber), while according to the original experiments of Fritschi, who carried out the hydrogenation in the presence of very little platinum, a more degraded and somewhat cyclicized hydrorubber is obtained. The saturated hydrorubber is much more stable than the unsaturated rubber since the loosening action of the double bonds is lacking. A hydrorubber of the average molecular weight of 10,000 is still relatively stable at 270°, while a hemi-colloidal rubber with this molecular weight will he cracked to still smaller fragments at this temperature, and these fragments are then changed by cyclicization. This behavior can be clearly seen in methylrubber. The following reduction proves that it is even more easily decomposed than rubber itself. With nickel as catalyst, Geiger obtained from methylrubber by reduction at 270° and 100 atmospheres a hemi-colloidal hydromethylrubber which had an average molecular weight of 1600 and therefore had a degree of polymerization of about 20. If rubber is reduced under the same conditions a higher molecular product is obtained with an average molecular weight of 3000 to 10,000. Judged by reduction experiments, the chain of butadiene rubber is still more stable, since the hydrobutadiene rubber prepared under the same conditions had the highest average molecular weight. The cleavage of the chains, as in the following formula, is therefore favored by the methyl groups:

Observations of the Thermal Decomposition of Brucite

1968 ◽  
Vol 26 ◽  
pp. 446-447
Author(s):  
P. L. Burnett ◽  
W. R. Mitchell ◽  
C. L. Houck
Keyword(s):  
Thermal Decomposition ◽  
Magnesium Oxide ◽  
Basal Plane ◽  
Magnesium Ions ◽  
A Value ◽  
Reaction Proceeds

Natural Brucite (Mg(OH)2) decomposes on heating to form magnesium oxide (MgO) having its cubic ﹛110﹜ and ﹛111﹜ planes respectively parallel to the prism and basal planes of the hexagonal brucite lattice. Although the crystal-lographic relation between the parent brucite crystal and the resulting mag-nesium oxide crystallites is well known, the exact mechanism by which the reaction proceeds is still a matter of controversy. Goodman described the decomposition as an initial shrinkage in the brucite basal plane allowing magnesium ions to shift their original sites to the required magnesium oxide positions followed by a collapse of the planes along the original <0001> direction of the brucite crystal. He noted that the (110) diffraction spots of brucite immediately shifted to the positions required for the (220) reflections of magnesium oxide. Gordon observed separate diffraction spots for the (110) brucite and (220) magnesium oxide planes. The positions of the (110) and (100) brucite never changed but only diminished in intensity while the (220) planes of magnesium shifted from a value larger than the listed ASTM d spacing to the predicted value as the decomposition progressed.

Gold liposomes

1996 ◽  
Vol 54 ◽  
pp. 898-899
Author(s):  
James F. Hainfeld
Keyword(s):  
Direct Methods ◽  
Important Class ◽  
Double Bonds ◽  
Membrane Phospholipids ◽  
Essential Ingredient ◽  
Lipid Structures

Lipids are an important class of molecules, being found in membranes, HDL, LDL, and other natural structures, serving essential roles in structure and with varied functions such as compartmentalization and transport. Synthetic liposomes are also widely used as delivery and release vehicles for drugs, cosmetics, and other chemicals; soap is made from lipids. Lipids may form bilayer or multilammellar vesicles, micelles, sheets, tubes, and other structures. Lipid molecules may be linked to proteins, carbohydrates, or other moieties. EM study of this essential ingredient of life has lagged, due to lack of direct methods to visualize lipids without extensive alteration. OsO4 reacts with double bonds in membrane phospholipids, forming crossbridges. This has been the method of choice to both fix and stain membranes, thus far. An earlier work described the use of tungstate clusters (W11) attached to lipid moieties to form lipid structures and lipid probes.

Field-assisted ionization theory for microscopists

1994 ◽  
Vol 52 ◽  
pp. 820-821
Author(s):  
Patrick P. Camus
Keyword(s):  
Electric Field ◽  
Electron Tunneling ◽  
Ionization Probability ◽  
Critical Distance ◽  
Tunneling Probability ◽  
Field Ionization ◽  
Radius Of Curvature ◽  
Field Evaporation ◽  
A Value ◽  
Ion Emission

The theory of field ion emission is the study of electron tunneling probability enhanced by the application of a high electric field. At subnanometer distances and kilovolt potentials, the probability of tunneling of electrons increases markedly. Field ionization of gas atoms produce atomic resolution images of the surface of the specimen, while field evaporation of surface atoms sections the specimen. Details of emission theory may be found in monographs.Field ionization (FI) is the phenomena whereby an electric field assists in the ionization of gas atoms via tunneling. The tunneling probability is a maximum at a critical distance above the surface,xc, Fig. 1. Energy is required to ionize the gas atom at xc, I, but at a value reduced by the appliedelectric field, xcFe, while energy is recovered by placing the electron in the specimen, φ. The highest ionization probability occurs for those regions on the specimen that have the highest local electric field. Those atoms which protrude from the average surfacehave the smallest radius of curvature, the highest field and therefore produce the highest ionizationprobability and brightest spots on the imaging screen, Fig. 2. This technique is called field ion microscopy (FIM).

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