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.

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:

Estimation, from Swelling, of the Structural Contribution of Chemical Reactions to the Vulcanization of Natural Rubber. Part I. General Method

1964 ◽  
Vol 37 (2) ◽  
pp. 563-570 ◽  
Author(s):  
Bryan Ellis ◽  
G. N. Welding
Keyword(s):  
Molecular Weight ◽  
Natural Rubber ◽  
Chemical Reactions ◽  
Network Structure ◽  
Reference Data ◽  
Direct Method ◽  
High Elasticity ◽  
Rubber Part ◽  
Structural Contribution ◽  
General Method

Abstract A procedure is described for estimating indirectly the contribution of vulcanization reactions to the build-up of network structure. This method is useful with technically important vulcanizing systems for which no direct method of estimation has been found. Errors of the theory of high elasticity are avoided by using published results, such as those of Moore and Watson of direct chemical estimates obtained with a special vulcanizing system that is chemically well understood. Reliance on the theories of end correction and swelling is also avoided by using published experimental relations. The method is applicable to any linear primary polymer of arbitrary molecular weight and any suitable swelling liquid, for which the required reference data have been obtained.

Isoprene and Rubber. Part 29. High Molecular Hydrorubbers

1932 ◽  
Vol 5 (2) ◽  
pp. 136-140
Author(s):  
H. Staudinger ◽  
W. Feisst
Keyword(s):  
Molecular Weight ◽  
Catalytic Reduction ◽  
Molecular Form ◽  
Average Molecular Weight ◽  
Molecular Size ◽  
Decomposition Products ◽  
Molecular Weights ◽  
Rubber Part ◽  
Derivatives Of ◽  
Suitable Process

Abstract The molecular concept in organic chemistry is based upon the fact that the molecules, whose existence is proved by vapor density determinations, enter into chemical reactions as the smallest particles. If now it is assumed that organic molecular colloids like rubber are dissolved in dilute solution in molecular form then it must be proved that in the chemical transposition of macromolecules as well no change in the size of the macromolecules occurs. In the case of hemicolloids, therefore for molecular colloids with an average molecular weight of 1000 to 10,000, this has been proved by the reduction of polyindenes, especially of polysterenes, to hydroproducts with the same average molecular weight, and also by the fact that cyclorubbers do not change their molecular weight upon autoöxidation. The molecular weights of hemi-colloidal hydrocarbons are therefore invariable. This is much more difficult to prove in the case of rubber, although there are many more ways in which unsaturated rubber can be transposed than the stable polysterenes, polyindenes, and poly cyclorubbers. In most of the reactions with rubber, as in its action with nitrosobenzene, oxidizing agents, hydrogen halides, and halogens, an extensive decomposition takes place as a result of the instability of the molecule, which is referred to in another work. Therefore derivatives of rubber are not formed, but derivatives of hemi-colloidal decomposition products. The catalytic reduction of rubber in the cold appears to be the most suitable process of making it react without changing its molecular size in order to prove that in a chemical transposition its molecular weight remains the same.

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 Structure of Elastomers and Their Reactivity

1951 ◽  
Vol 24 (1) ◽  
pp. 95-98
Author(s):  
A. S. Kuz'minskii ◽  
N. N. Lezhnev
Keyword(s):  
Molecular Weight ◽  
Methyl Groups ◽  
Side Chains ◽  
Double Bonds ◽  
Gutta Percha ◽  
Different Temperatures ◽  
Spatial Configurations ◽  
The Mean ◽  
Kinetics Of ◽  
Mean Molecular Weight

Abstract It has not yet been ascertained what constituent parts within the structure of various elastomers have the greatest influence on the reactivity of the elastomers. There are indications that the side chains, the presence of methyl groups acting as substitutes, and differences in spatial configurations, etc., all have definite effects. The present authors have investigated the oxidation of several different elastomers at different temperatures. The experiments were carried out both in the presence and in the absence of an inhibitor (phenyl-β-naphthylamine). The elastomers and the inhibitor were first carefully purified. The kinetics of autoxidations were studied volumetrically by means of an apparatus already described by one of the authors. A chainless molecular introduction of oxygen into the double bonds of the elastomer in the presence of the inhibitor was studied with the aid of our own previously described inhibitor methods. The study included the oxidation of butadiene elastomers containing different distributions of double bonds in the main and side chains, divinylstyrene rubber, and the hydrocarbons of natural rubber and gutta-percha. These products are distinguished by their different degrees of unsaturation, the number of side chains, the number of double bonds in both their main and side chains, the length of their molecular chains (the mean molecular weight), and their spatial configurations.

Isoprene and Rubber. Part 41. The Hydrogenation of Rubber and Balata

1934 ◽  
Vol 7 (3) ◽  
pp. 496-502
Author(s):  
H. Staudinger ◽  
E. O. Leupold
Keyword(s):  
Molecular Weight ◽  
Particle Sizes ◽  
Colloidal Solutions ◽  
Uniform Size ◽  
Micellar Structure ◽  
Molecular Weights ◽  
Rubber Particles ◽  
Rubber Part ◽  
Points Of View ◽  
Molecular Substances

Abstract Viscosity measurements of dilute solutions of rubber and of balata led to the following values for the size and form of the molecules of these hydrocarbons. It is therefore not a question of definition whether the particle sizes shown above are to be regarded as the molecular or the micellar weights of these substances, for here the concept of molecular weight has the same significance as in the case of lower molecular substances, i. e., the molecule comprises the sum of all atoms combined by normal, i. e., homopolar atoms. The only difference between low and high molecular substances is that low molecular substances are composed of molecules of uniform size, whereas high molecular substances are a mixture of homologous polymers, so that the values above refer to average molecular weights. These results, which explain the nature of colloidal solutions of rubber, are at variance with the views of most investigators of colloids, who ascribe a micellar structure to the rubber particles, and in this way explain the property which rubber has of forming colloidal solutions. This makes clear why until very recently explanations of the constitution of rubber have been open to question among these particular investigators themselves. In order to lend further support to our opinion, the reduction of rubber and balata and low molecular homologous polymeric hydrocarbons was undertaken from certain points of view, as shown in the work which follows.

THE ANIONIC POLYMERIZATION OF ALLYL ACRYLATE AND OF ALLYL METHACRYLATE

1966 ◽  
Vol 44 (6) ◽  
pp. 695-702 ◽  
Author(s):  
S. Bywater ◽  
P. E. Black ◽  
D. AM. Wiles
Keyword(s):  
Molecular Weight ◽  
Anionic Polymerization ◽  
Allyl Alcohol ◽  
Polymer Chains ◽  
Cross Linking ◽  
Low Molecular Weight ◽  
Carbonyl Groups ◽  
Double Bonds ◽  
Soluble Product ◽  
Allyl Methacrylate

The low temperature polymerization of allyl acrylate in toluene solution has been investigated with n-butyllithium and 1,1-diphenyl-n-hexyllithium initiators. The latter was also used in a study of the polymerization of allyl methacrylate under the same conditions. The reactions between initiator and monomer were rapid in all cases. More than half of the initiator molecules reacted with monomer acrylic double bonds to start polymer chains, only a few of which grew to a high molecular weight, highly isotactic product. Most of the chains remained as a low molecular weight, precipitant-soluble product. The remaining initiator molecules reacted with the carbonyl groups of the monomers to produce species which could be detected as allyl alcohol, after termination of the reaction with acetic acid. The allyl double bonds were not involved in reactions during polymerization but were presumably responsible for the cross-linking which occurred when the polymers were exposed to air.

Isoprene and Rubber. Part 22. Isorubber Nitrone

1931 ◽  
Vol 4 (2) ◽  
pp. 191-200
Author(s):  
H. Staudinger ◽  
H. Joseph
Keyword(s):  
Molecular Weight ◽  
High Molecular Weight ◽  
Dilute Solution ◽  
Solid Substance ◽  
Phosphonium Salts ◽  
Parent Molecule ◽  
Solution Form ◽  
Rubber Part ◽  
A Chain ◽  
Very High

Abstract Rubber Micelles or Macromolecules The idea of Pummerer that the parent molecule of rubber is [C5C8]8 is based upon molecular weight determinations carried out by him and his colleagues upon rubber in menthol and above all upon isorubber nitrone. This latter product, which has been prepared by Alessandri and again by Bruni and Geiger by the action of nitrosobenzene on rubber has, according to Pummerer and Gündel, the constitution [C5H6,C6H5NO]8. On this subject the authors say that: We made cryoscopic molecular weight determinations of isorubber nitrone iii benzene and nitrobenzene. Even in these generally used solvents the nitrone gives depressions which indicate a molecular weight lying between 1200 and 1400. For a parent rubber molecule of 8 isoprenes which reacts with 8 molecules of nitrosobenzene with a splitting off of 16 atoms of water, a weight of 1384 is calculated, agreeing very well with the above. As is the case with determinations of rubber in menthol, here the final measurements can be undertaken only when the constant is obtained (in this case after 1-2 hours) and not immediately after the solid substance disappears, for otherwise the value will be about 1000 or 2000 higher, which probably results from a still incomplete solution of the micelles. The study of isorubber nitrone, therefore, supports our opinion on the size of the parent rubber molecule which was expressed earlier. These opinions apparently do not conform to the view expressed by one of us some time ago, according to which rubber has a very high molecular weight, and the primary colloid particles, therefore, the particles in dilute solution, form macromolecules. These have a molecular weight of about 68,000, so that approximately 1000 isoprene residues are united in a chain . This concept was based on a study of models, especially on experiments on polysterol and further by conversion of rubber into colloid-soluble rubber-phosphonium salts, by the preparation of homologous polymeric series of polyprenes, by the decomposition of rubber, and finally by relations between viscosity and molecular weight in this series.

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