Polymeric Unsaturation and Relative Rate of Cross-Linkage

1949 ◽  
Vol 22 (1) ◽  
pp. 16-36
Author(s):  
R. L. Zapp
Keyword(s):  
Relative Rate ◽  
Polymer Networks ◽  
Cross Linking ◽  
Active Centers ◽  
Tetramethylthiuram Disulfide ◽  
Volume Increase ◽  
Cross Linkage ◽  
Constant State ◽  
Cross Links ◽  
The Difference

Abstract In conventional vulcanization reactions with sulfur and accelerator, the rate as well as the extent of cross-linking to form polymer networks depends on the concentration of chemical unsaturation. The purpose of this paper was to determine the relationships between polymeric unsaturation and the rate of vulcanization. The course of the cross-linking reaction was followed by volume swelling measurements converted to a relative cross-linked index; this index is shown to be directly related to extension modulus before the onset of crystallization. Experimental evidence with a system of polymer, zinc oxide, sulfur, and tetramethylthiuram disulfide closely approaches the hypothesis, based on the possible paths of cross-linkage between adjacent chains. The experimental equation, at constant relative cross-links of 18.2 at 1000 per cent volume increase in cyclohexane, is t=c/n1.8 when adjustments are applied. When a system utilizing benzothiazyl monocyclohexyl sulfenamide is studied, the time to a constant state of vulcanization is related to the reciprocal of the first power of the unsaturation, t=c/n. In both relations, t is time, n is the polymeric unsaturation, and c is a constant which depends on the temperature and state of cure. The difference in response to polymeric unsaturation by these two types of accelerators is reflected in the percentage of combined sulfur for a given concentration of cross-links (state of cure). The thiuram requires less combined sulfur for a given state of vulcanization than does the thiazole, whereas a nonaccelerated mixture requires still more combined sulfur for a given state of cure. In an attempt to rationalize the differences in accelerator behavior, four points are discussed which involve the concepts of active centers, carbon-carbon linkages, varying porportions of sulfur in a carbon-sulfur-carbon bridge, and consideration of inter- and intramolecular linkages.

Studies of the Vulcanization of Rubber

1952 ◽  
Vol 25 (2) ◽  
pp. 209-229 ◽  
Author(s):  
Shu Kambara ◽  
Kumakazu Ohkita
Keyword(s):  
Organic Compounds ◽  
Chemical Structure ◽  
Room Temperature ◽  
Great Influence ◽  
Cross Linking ◽  
Oxidizing Agent ◽  
Vulcanized Rubber ◽  
Cross Linkage ◽  
Bridge Type ◽  
The Difference

Abstract In this study much information about the method of distinguishing the state in which sulfur is combined in simple organic compounds consisting of carbon, hydrogen, and sulfur was obtained, and a new theory of vulcanization was postulated as a result of its application to vulcanized rubber. When activated sulfur reacts with rubber, it first adds to the double bonds, forming thioketones, which in turn, as a characteristic of these radicals, combine with each other, with the formation of a thioether structure. This transformation of thioketone into thioether takes place, not only during vulcanization, but also gradually after vulcanization. Because of the presence of thioketone, treatment of vulcanized rubber with hydrazine, forms a new network, that is, a ketoazine cross-linkage. Combined sulfur of the thioketone type was determined by an oxidizing agent, and as the difference of this value and total combined sulfur a method of determining bridge type of combined sulfur has been proposed. By this method, it was found that, even in ebonite, about one-third of the combined sulfur is the thioketone type, and that the bridge type is only about two-thirds of the total. The thioketone type of combined sulfur in soft vulcanized rubber is transformed gradually into the thioether type of cross-linkage when allowed to stand at room temperature, and this transformation is accelerated when the temperature is raised. In the case of hard rubber, this phenomenon is also observable, but the rate of this transformation is much slower compared to the former. This tendency is the same in the case of ketoazine cross-linking when rubber vulcanizates are treated with hydrazine. From these facts, it seems that the distribution of the thioketone radicals is not uniform, and the magnitude of the probability for collision of these radicals to form cross-linkages has a great influence on the properties of rubber after vulcanization. That is, the property of the vulcanizate is greatly affected by the fact whether the thioketone radicals in the vulcanizates are comparatively uniformly distributed or whether they exist in sectional groups or in colonies. The authors are the first to advance this postulate concerning the chemical structure of vulcanized rubber and its transformation. We believe that when the study is extended, using this postulation, problems such as aging and the differences in the properties of vulcanized rubber accelerated with various accelerators will become clear. Moreover, we believe that it will be of interest to physicists studying rubber elasticity to suggest this idea of colony of cross-linkages. We are now carrying on researches on these problems, and we shall report on them later.

Collagen Cross-linking and Ultimate Tensile Strength in Dentin

2004 ◽  
Vol 83 (10) ◽  
pp. 807-810 ◽  
Author(s):  
P.A. Miguez ◽  
P.N.R. Pereira ◽  
P. Atsawasuwan ◽  
M. Yamauchi
Keyword(s):  
Tensile Strength ◽  
Ultimate Tensile Strength ◽  
Dental Materials ◽  
Cross Linking ◽  
Anatomical Location ◽  
Dentinal Tubules ◽  
Root Dentin ◽  
Cross Links ◽  
The Difference ◽  
Collagen Cross Linking

Several studies have indicated differences in bond strength of dental materials to crown and root dentin. To investigate the potential differences in matrix properties between these locations, we analyzed upper root and crown dentin in human third molars for ultimate tensile strength and collagen biochemistry. In both locations, tensile strength tested perpendicular to the direction of dentinal tubules (undemineralized crown = 140.4 ± 48.6/root = 95.9 ± 26.1; demineralized crown = 16.6 ± 6.3/root = 29.0 ± 12.4) was greater than that tested parallel to the tubular direction (undemineralized crown = 73.1 ± 21.2/root = 63.2 ± 22.6; demineralized crown = 9.0 ± 3.9/root = 16.2 ± 8.0). The demineralized specimens showed significantly greater tensile strength in root than in crown. Although the collagen content was comparable in both locations, two major collagen cross-links, dehydrodihydroxylysinonorleucine/its ketoamine and pyridinoline, were significantly higher in the root (by ~ 30 and ~ 55%, respectively) when compared with those in the crown. These results indicate that the profile of collagen cross-linking varies as a function of anatomical location in dentin and that the difference may partly explain the site-specific tensile strength.

Stoichiometry of Vulcanization with Sulfur

1951 ◽  
Vol 24 (4) ◽  
pp. 878-893
Author(s):  
R. L. Zapp ◽  
R. H. Decker ◽  
Margaret S. Dyroff ◽  
Harriet A. Rayner
Keyword(s):  
Physical Properties ◽  
Polymer Networks ◽  
Diazo Compounds ◽  
Polymerization Process ◽  
Cross Linking ◽  
High Chemical ◽  
Chemical Combination ◽  
Cross Linkage ◽  
Vulcanization Process ◽  
Butadiene Styrene

Abstract In the study of vulcanization with natural rubber and other polymers of relatively high chemical unsaturation, it has always been difficult to represent the vulcanization process molecularly because of the complexity of the sulfur-polymer reactions. To circumvent this difficulty, reactions of small olefin molecules with sulfur have often been studied to obtain this molecular insight. Some investigators have resorted to cross-linking the polymer with agents other than sulfur to characterize the network for comparisons with physical properties. By cross-linking rubber molecules with diazo compounds, which add quantitatively to the olefin bond, Flory has characterized the network so formed in a molecular manner and correlated the degree of cross-linking with physical properties. When correlating physical properties with degree of cross-linking in butadiene-styrene polymers, others have cross-linked the polymer as a final step in the polymerization process. When a polymer of low unsaturation is used, many of the experimental difficulties are eliminated or reduced, and a more reliable stoichiometric picture of the phenomenon can be obtained. The emphasis in this work is placed on the chemical combination of sulfur with polymer rather than on any correlation with physical properties, and rests upon the “dimensions” of swollen polymer networks as related to total combined and organically combined sulfur. The low unsaturation of Butyl rubber makes it possible to satisfy all the potential points of cross-linkage while still possessing a network that is soft and elastic. In actual practice, there probably is a small percentage of the reactive sites or points of unsaturation disposed in such a way that they cannot approach an active site in another molecule. Experimentally, however, one can obtain a “maximum” state of vulcanization where further vulcanization time or additional sulfur and accelerator do not contribute further to additional cross-linkage. This feature is utilized in the present investigations.

scholarly journals Non-enzymic glycation of collagen inhibits binding of oxidized low-density lipoprotein

1993 ◽  
Vol 293 (3) ◽  
pp. 661-666 ◽  
Author(s):  
N Kalant ◽  
S McCormick ◽  
M A Parniak
Keyword(s):  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Cross Linking ◽  
Low Density ◽  
Collagen Gels ◽  
Oxidized Low Density Lipoprotein ◽  
Agarose Beads ◽  
Cross Links ◽  
The Difference ◽  
Intermolecular Distances

We have examined the effect of non-enzymic glycation of native soluble collagen, in solution or in gels, on binding of oxidized low-density lipoprotein (LDL). We found the following. (1) Glycation markedly inhibited binding of LDL. This is contrary to results previously reported; the difference may be attributable to the use of detergent- and heat-denatured collagen, covalently bound to agarose beads, in the earlier study. (2) With increased duration of glycation, collagen solution would not gel, and preformed gels dissolved. (3) [14C]Glucose bound to collagen gels dissociated slowly, even at pH 5, suggesting that it was not present as a Schiff's base; in addition, ketoamines, pentosidine and fluorescent advanced glycation products were not detectable in glycated collagen gels, although they accumulated in tendon collagen glycated under the same conditions. It is hypothesized that the difference in glycation effects between gel and tendon may be due to the strength of cross-linking before glycation: the increase in intermolecular distance in collagen fibrils which results from glycation disrupts the fibrils in gels, preventing binding of LDL and formation of glycation-dependent cross-links, whereas the extensive cross-linking in tendon maintains the intermolecular distances within a range which permits formation of glycation cross-links.

Model Elastomers

1997 ◽  
Author(s):  
Burak Erman ◽  
James E. Mark
Keyword(s):  
Molecular Weight ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Polymer Networks ◽  
Length Distribution ◽  
Quantitative Information ◽  
Cross Linking ◽  
Cross Links ◽  
End Linking ◽  
The Cross

Until quite recently, there was relatively little reliable quantitative information on the relationship of stress to structure, primarily because of the uncontrolled manner in which elastomeric networks were generally prepared. Segments close together in space were linked irrespective of their locations along the chain trajectories, thus resulting in a highly random network structure in which the number and locations of the cross-links were essentially unknown. Such a structure is shown in figure 10.1. New synthetic techniques are now available, however, for the preparation of “model” polymer networks of known structure. More specifically, if networks are formed by end linking functionally terminated chains instead of haphazardly joining chain segments at random, then the nature of this very specific chemical reaction provides the desired structural information. Thus, the functionality of the cross links is the same as that of the end-linking agent, and the molecular weight Mc between cross-links and the molecular weight distribution are the same as those of the starting chains prior to their being end-linked. An example is the reaction shown in figure 10.2, in which hydroxyl-terminated chains of poly(dimethylsiloxane) (PDMS) are end-linked using tetraethyl orthosilicate. Characterizing the un-cross-linked chains with respect to molecular weight Mn and molecular weight distribution, and then carrying out the specified reaction to completion, gives elastomers in which the network chains have these characteristics; in particular, a molecular weight Mc between cross-links equal to Mn, a network chain-length distribution equal to that of the starting chains, and cross-links having the functionality of the end-linking agent. It is also possible to use chains having a known number of potential cross-linking sites placed as side chains along the polymer backbone, so long as their distribution is known as well. Because of their known structures, such model elastomers are now the preferred materials for the quantitative characterization of rubberlike elasticity. Such very specific cross-linking reactions have also been shown to be useful in the preparation of liquid-crystalline elastomers. Trifunctional and tetrafunctional PDMS networks prepared in this way have been used to test the molecular theories of rubber elasticity with regard to the increase in non-affineness of the network deformation with increasing elongation.

Cross-Linking in Natural-Rubber Vulcanizates

1953 ◽  
Vol 26 (4) ◽  
pp. 741-758 ◽  
Author(s):  
H. E. Adams ◽  
B. L. Johnson
Keyword(s):  
Molecular Weight ◽  
Natural Rubber ◽  
Cross Linking ◽  
Cross Link ◽  
General Validity ◽  
Tetramethylthiuram Disulfide ◽  
Cross Links ◽  
The Cross ◽  
Natural Rubber Vulcanizates ◽  
The Relationship

Abstract Recently, a method for measuring the average number of cross-links per chain of vulcanized polymer has been developed. It is possible to calculate the degree of cross-linking of the vulcanizate from its amount of swelling in a solvent such as benzene. This method was used by Flory to study the effect of primary molecular weight on the cross-linking of Butyl vulcanizates. An evaluation of the general validity of the method was ascertained by using quantitative cross-linking agents (diazodicarboxylates) to prepare vulcanizates of natural rubber and GR-S. Bardwell and Winkler have also used this technique to study the relationship between the degree of cross-linking and the force of retraction at 300 per cent elongation of GR-S latex vulcanized with potassium persulfate. The formation of cross-linking during the vulcanization by sulfur of several polymers has also been investigated. Gee has compared the formation of cross-linking in natural rubber vulcanizates with the amount of combined sulfur. Carbon-to-carbon cross-links were believed to be formed in a nonsulfur tetramethylthiuram disulfide (TMTD) cure. A similar study of Butyl rubber vulcanizates, cured with sulfur-TMTD, indicates that disulfide cross-links are formed. Scott and Magat have estimated that eight sulfur atoms are associated with each cross-link in Russian SK (sodium polybutadiene). This investigation was undertaken to extend Gee's study on the correlation of the cross-linking of natural-rubber vulcanizates with the amount of combined sulfur.

scholarly journals Chemistry of collagen cross-links: glucose-mediated covalent cross-linking of type-IV collagen in lens capsules

1993 ◽  
Vol 296 (2) ◽  
pp. 489-496 ◽  
Author(s):  
A J Bailey ◽  
T J Sims ◽  
N C Avery ◽  
C A Miles
Keyword(s):  
Type Iv Collagen ◽  
Cross Linking ◽  
Mechanical And Thermal Properties ◽  
Maximum Strain ◽  
Scanning Calorimetry ◽  
Melting Temperatures ◽  
Type Iv ◽  
Collagen Molecules ◽  
Cross Links

The incubation of lens capsules with glucose in vitro resulted in changes in the mechanical and thermal properties of type-IV collagen consistent with increased cross-linking. Differential scanning calorimetry (d.s.c.) of fresh lens capsules showed two major peaks at melting temperatures Tm 1 and Tm 2 at approx. 54 degrees C and 90 degrees C, which can be attributed to the denaturation of the triple helix and 7S domains respectively. Glycosylation of lens capsules in vitro for 24 weeks caused an increase in Tm 1 from 54 degrees C to 61 degrees C, while non-glycosylated, control incubated capsules increased to a Tm 1 of 57 degrees C. The higher temperature required to denature the type-IV collagen after incubation in vitro suggested increased intermolecular cross-linking. Glycosylated lens capsules were more brittle than fresh samples, breaking at a maximum strain of 36.8 +/- 1.8% compared with 75.6 +/- 6.3% for the fresh samples. The stress at maximum strain (or ‘strength’) was dramatically reduced from 12.0 to 4.7 N.mm.mg-1 after glycosylation in vitro. The increased constraints within the system leading to loss of strength and increased brittleness suggested not only the presence of more cross-links but a difference in the location of these cross-links compared with the natural lysyl-aldehyde-derived cross-links. The chemical nature of the fluorescent glucose-derived cross-link following glycosylation was determined as pentosidine, at a concentration of 1 pentosidine molecule per 600 collagen molecules after 24 weeks incubation. Pentosidine was also determined in the lens capsules obtained from uncontrolled diabetics at a level of about 1 per 100 collagen molecules. The concentration of these pentosidine cross-links is far too small to account for the observed changes in the thermal and mechanical properties following incubation in vitro, clearly indicating that another as yet undefined, but apparently more important cross-linking mechanism mediated by glucose is taking place.

scholarly journals Cross-linking of the electron-transfer flavoprotein to electron-transfer flavoprotein-ubiquinone oxidoreductase with heterobifunctional reagents

1988 ◽  
Vol 255 (3) ◽  
pp. 869-876 ◽  
Author(s):  
D J Steenkamp
Keyword(s):  
Electron Transfer ◽  
Small Subunit ◽  
Cross Linking ◽  
Minor Effect ◽  
Electron Transfer Flavoprotein ◽  
Ubiquinone Oxidoreductase ◽  
Lysine Residues ◽  
Cross Links ◽  
A Minor ◽  
Chemical Cross Linking

The mitochondrial electron-transfer flavoprotein (ETF) is a heterodimer containing only one FAD. In previous work on the structure-function relationships of ETF, its interaction with the general acyl-CoA dehydrogenase (GAD) was studied by chemical cross-linking with heterobifunctional reagents [D. J. Steenkamp (1987) Biochem. J. 243, 519-524]. GAD whose lysine residues were substituted with 3-(2-pyridyldithio)propionyl groups was preferentially cross-linked to the small subunit of ETF, the lysine residues of which had been substituted with 4-mercaptobutyramidine (MBA) groups. This work was extended to the interaction of ETF with ETF-ubiquinone oxidoreductase (ETF-Q ox). ETF-Q ox was partially inactivated by modification with N-succinimidyl 3-(2-pyridyldithio)propionate to introduce pyridyl disulphide structures. A similar modification of ETF caused a large increase in the apparent Michaelis constant of ETF-Q ox for modified ETF owing to the loss of positive charge on some critical lysines of ETF. When ETF-Q ox was modified with 2-iminothiolane to introduce 4-mercaptobutyramidine groups, only a minor effect on the activity of the enzyme was observed. To retain the positive charges on the lysine residues of ETF, pyridyl disulphide structures were introduced by treating ETF with 2-iminothiolane in the presence of 2,2′-dithiodipyridyl. The electron-transfer activity of the resultant ETF preparation containing 4-(2-pyridyldithio)butyramidine (PDBA) groups was only slightly affected. When ETF-Q ox substituted with MBA groups was mixed with ETF bearing PDBA groups, at least 70% of the cross-links formed between the two proteins were between the small subunit of ETF and ETF-Q ox. ETF-Q ox, therefore, interacts predominantly with the same subunit of ETF as GAD. Variables which affect the selectivity of ETF-Q ox cross-linking to the subunits of ETF are considered.

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