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 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.

Mechanism of Rubber Vulcanization with Sulfur

1938 ◽  
Vol 11 (1) ◽  
pp. 107-130
Author(s):  
W. K. Lewis ◽  
Lombard Squires ◽  
Robert D. Nutting
Keyword(s):  
Natural Rubber ◽  
Temperature Coefficient ◽  
Chemical Reactions ◽  
Chemical Reaction ◽  
Reaction Rate ◽  
Complex Behavior ◽  
Double Bonds ◽  
Irreversible Reaction ◽  
Sulfur Addition

Abstract THAT vulcanization of rubber with sulfur always involves a chemical reaction consisting in the addition of sulfur to the double bonds of the rubber molecule has been conclusively established (18, 28). The facts indicate that this addition of sulfur to rubber is an irreversible reaction (31). The temperature coefficient of the reaction is high, increasing about 2.65 fold per 10° C. at ordinary curing temperatures (31). Furthermore, the reaction is apparently exothermic (4, 24). It is noteworthy that catalysts are apparently necessary, since synthetic rubbers prepared from pure materials add sulfur slowly, if at all. The proteins and perhaps the resins in natural rubber undoubtedly serve as accelerators. The curves for combined sulfur vs. time of cure for typical mixes are shown in Figures 1 and 2. Figure 1 is taken from the data of Kratz and Flower (16); the composition and temperature of cure for this mix are shown in Cranor's Table I (9). Figure 2, curve 1, is from Table I of Eaton and Day (10), and curve 2 from data obtained in this laboratory (27, Table I). Superficial inspection of these curves shows extraordinary divergence of type. Figure 1 is a typical fadeaway curve, characteristic of most chemical reactions, where the reaction rate decreases with decreasing concentration of the reacting materials. Curve 1, Figure 2, is an entirely different type, where the rate of sulfur addition is constant until nearly 70 per cent of the initial sulfur has reacted. Curve 2, Figure 2, shows even more complex behavior. Again the rate is constant in the initial portions of the cure. However, following this period, the rate increases markedly but later falls off, approaching zero, to give an S-shaped eurve.

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 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.

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.

Measurement of Internal Double Bonds in Polymers by Perbenzoic Acid Addition

1948 ◽  
Vol 21 (4) ◽  
pp. 821-829 ◽  
Author(s):  
Alfred Saffer ◽  
B. L. Johnson
Keyword(s):  
Double Bond ◽  
Low Ph ◽  
Side Chain ◽  
Double Bonds ◽  
Extrapolation Procedure ◽  
Perbenzoic Acid ◽  
Acid Methyl ◽  
Emulsion Polymers ◽  
Small Excess ◽  
Minimum Interference

Abstract Internal double bonds formed by 1,4-polymerization of diene monomers add perbenzoic acid more rapidly than do vinyl double bonds which are the products of the 1,2-type of addition. The extrapolation procedure proposed for determining internal double bond contents of diene polymers is based on this difference in addition rates. Oleic acid mixtures with 10-undeeylenie acid were prepared and analyzed with an accuracy of 1 per cent. However, the method is limited to systems containing 70 per cent or more internal double bonds. Minimum interference of side-chain oxidation by perbenzoic acid was attained by using a low temperature and a small excess of perbenzoic acid. Methyl-substituted emulsion polymers are characterized by high amounts of 1,4-addition. Polymerizations with alkali-metal catalysts result in products of high vinyl double-bond content. A slight preference for the 1,4-type of polymerization is favored in media of low pH. Natural rubbers are formed almost completely by 1,4-polymerization. Heat softening, modifier concentration, and extent of conversion do not influence the degree of 1,4-polymerization.

Oxidation of Photoexcited Elastomers

1972 ◽  
Vol 45 (2) ◽  
pp. 481-518 ◽  
Author(s):  
Mme J. L. Morand
Keyword(s):  
Free Radicals ◽  
Linear Function ◽  
Initial Rate ◽  
Incident Light ◽  
Double Bonds ◽  
Photophysical Process ◽  
Vulcanized Rubber ◽  
The One ◽  
Limiting Value ◽  
Butadiene Styrene

Abstract The sensitivity spectrum of elastomers to sunlight (λ≽300 nm), determined by the variation at 30° C of the initial rate of oxidation or chain scissions as a function of the wavelength of incident light, shows several maxima in the near UV. These maxima are approximately equidistant and the space between them differs only slightly (10 to 11.5 nm) according to the polydienes (polyisoprene, polybutadiene, copolymer butadiene-styrene) in the crude or the vulcanized state, whatever may be the curing system. The identified maxima, existing also under vacuum (10−4 Torr), can be due to the presence of some chromophores in the chains. The latter, in absorbing the light during the primary photophysical process, would initiate the degradation. Among different possibilities, an S0→T1 transition of the isolated double bonds, producing free radicals, seems to be the one likely to explain the results. After the initiation, the photoxidation at 30° C and 5 mW/cm2 proceeds like the thermoxidation near 150° C. For a peroxide vulcanized rubber, the kinetics are similar and the rates of oxidation are somewhat faster under the most harmful sunrays than those observed by Bevilacqua at 120° C. Moreover, the chain scissions are a linear function of the oxygen consumed and their ratio is close to the limiting value of about 6 moles of O2 per broken bond, obtained by this author at 140–150° C.

The Chemical Structure of the “Popcorn” Polymer of Butadiene

1958 ◽  
Vol 31 (3) ◽  
pp. 581-587
Author(s):  
A. I. Yakubchik ◽  
A. I. Spasskova
Keyword(s):  
Chemical Structure ◽  
Relative Content ◽  
Double Bonds ◽  
Soluble Polymer ◽  
Degree Of Unsaturation ◽  
Rubbery Polymers

Abstract 1. The chemical structure of spongy butadiene polymer, obtained at 15–20° was examined by the ozonolysis method. 2. The per cent of chains with external double bonds in the spongy polymer was found to be 22.8%. 3. The spongy polymer of butadiene is composed, like the rubbery polymers, of chains with external and internal double bonds. 4. It was established that parts of the molecule of spongy polymer have the same structure as the rubbery butadiene polymers: -1,4-1,4-; -1,4-1,2-1,4-; -1,4-1,2-1,2-1,4-. 5. A chloroform-soluble rubberlike polymer was separated from the butadiene autopolymer. The degree of unsaturation of the chloroform-soluble polymer was determined (86.7%), also the relative content of internal and external double bonds.

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