Polybutadiene Vulcanization. Chemical Structures from Sulfur-Donor Vulcanization of an Accurate Model

1984 ◽  
Vol 57 (5) ◽  
pp. 1056-1097 ◽  
Author(s):  
Earl C. Gregg ◽  
Robert P. Lattimer
Keyword(s):  
Network Structure ◽  
Crosslink Density ◽  
Hydrogen Transfer ◽  
Reaction Products ◽  
Volatile Substances ◽  
Chemical Structures ◽  
Trans Isomerization ◽  
Polybutadiene Rubber ◽  
Configurational Isomerism ◽  
Crosslinking Agents

Abstract Only 1,5-polyenes with three or more double bonds crosslinked in a curing recipe with 2-benzothiazolyl-N-morpholyl disulfide (BMD) or bis(dimethylthiocarbamyl) disulfide (TMTD) as the crosslinking agents. A suitable chemical model for 1,4-polybutadiene (PB) is cycIohexadeca-1,5,9,13-tetraene (CHT). The preparation of CHT is described. The crosslink density of a CHT vulcanizate agreed well with the chemical crosslink density of cis- 1,4-polybutadiene rubber, similarly cured. The crosslink density of the CHT vulcanizate was measured by isolating, identifying, and weighing the various crosslink structures. The non-crosslink structures of the network and the extranetwork structures were also identified and quantified. Various amounts of curative fragments attach to the PB network structure, as exemplified by the amount of curative fragments attached to CHT. About 16% of the lauric acid attached to the network structure. The curing agent, BMD, divided into three fragments: 2-thiobenzothiazole, morpholyl, and thio groups. About 67% of the thio groups, 25% of the 2-thiobenzothiazole groups, and about 6% of the morpholyl groups attached to the network structure. About 57% of the thio groups formed crosslinks. The main crosslink structure was 85% bis(allylic) monosulfide and 15% bis(allylic) disulfide. The length of the disulfide crosslink was only 60 pm greater than the length of the monosulfide crosslink. This compares with the 0.2 nm length of a sulfur atom. Very little cis-trans isomerization occurred in the unreacted CHT as a result of vulcanization. This indicated almost no cis-trans isomerization of unreacted segments of PB in PB vulcanizates. However, extensive cis-trans isomerization occurred in the CHT that crosslinked, which indicates that cis-trans isomerization in PB vulcanizates is confined to the reaction sites of the PB molecules. The configurational isomerism was essentially exclusively cis-to-trans. No trans-to-cis isomerism was observed. The insoluble solid in the vulcanizate was a mixture of cadmium bis(2-thiobenzothiazole), cadmium sulfide, and morpholinium sulfate. Material balances of the reaction products with the curatives showed that 90% by weight of the reaction products of the vulcanization of CHT were identified. The hydrogen transfer balance showed that CHT is the main hydrogen donor during crosslink formation. The morpholyl group from BMD was the main hydrogen acceptor and formed morpholine and morpholinium sulfate. Escape of volatile substances during vulcanization of PB resulted in much reduced crosslinking. For this reason, a hydraulic reactor for vulcanization of liquids, such as CHT, without loss of volatile substances was described.

The Crystallization of Modified Cis-Polybutadiene

1960 ◽  
Vol 33 (3) ◽  
pp. 699-702
Author(s):  
G. S. Trick
Keyword(s):  
Melting Point ◽  
Crosslink Density ◽  
Fixed Temperature ◽  
Trans Isomerization

Abstract From a sample of polybutadiene of high cis-1,4 content, the microstructure is modified by cis-trans isomerization or by crosslinking. Measurements of rates of crystallization and melting point are made on the modified samples. An increase in irons content or crosslink density markedly decreases the rate of crystallization at a fixed temperature. It is found, however, that this retardation in rate may usually be accounted for by the depressed melting point of the modified samples.

scholarly journals Recent Observations on the Mechanical Properties of Polymer Networks

1971 ◽  
Vol 44 (5) ◽  
pp. 1256-1272 ◽  
Author(s):  
P. Thirion ◽  
R. Chasset
Keyword(s):  
Crosslink Density ◽  
Room Temperature ◽  
Dynamic Properties ◽  
Polymer Networks ◽  
The Other ◽  
Dilution Ratio ◽  
Chain Entanglement ◽  
Influence Of Temperature ◽  
Terminal Zone ◽  
Crosslinking Agents

Abstract The influence of temperature, elongation, swelling or dilution ratio, crosslink density, nature of the polymers, and crosslinking agents on the dynamic properties, creep and relaxation of polymer networks is surveyed in the terminal region of the spectrum. Whereas the deformation does not change the relaxation kinetics in large ranges of extension, the crosslink density acts as a reduced variable apparently accelerating uniformly the viscoelastic processes beyond the glass transition. The other possible reductions ‘time-temperature’ and ‘time—swelling’ do not necessarily seem related to the variations of free volume. From the viewpoint of the explanation of the relaxation mechanisms in the terminal zone, the fact that the equilibrium of loosely crosslinked elastomers would only virtually be reached after several years at room temperature seem in better agreement with chain entanglement effects, either trapped or not by the permanent network, than with the dissociation of secondary linkages.

scholarly journals Chemical Structures of Novel Maillard Reaction Products under Hyperglycemic Conditions

2018 ◽  
Vol 66 (4) ◽  
pp. 363-367 ◽  
Author(s):  
Daisuke Imahori ◽  
Takahiro Matsumoto ◽  
Naoto Kojima ◽  
Tomohiro Hasei ◽  
Megumi Sumii ◽  
...  
Keyword(s):  
Maillard Reaction ◽  
Maillard Reaction Products ◽  
Reaction Products ◽  
Chemical Structures

Pre-Vulcanization Inhibition of a N-t-Butyl-2-Benzothiazole Sulfenamide Cure by N-(Cyclohexylthio)Phthalimide

2004 ◽  
Vol 77 (5) ◽  
pp. 931-946 ◽  
Author(s):  
M. H. S. Gradwell ◽  
N. R. Stephenson
Keyword(s):  
Zinc Oxide ◽  
Crosslink Density ◽  
Decomposition Product ◽  
Crosslinking Reaction ◽  
Rapid Rise ◽  
Reaction Products ◽  
Presence And Absence

Abstract The reactions of N-(cyclohexylthio)phthalimide (CTP), in the absence of zinc oxide, leading to the inhibition of vulcanization in a N-t-butyl-2-benzothiazole sulfenamide (TBBS) accelerated sulfur cure were studied in the presence and absence of rubber. Mixtures of CTP, TBBS and sulfur were heated in a DSC and the reaction products and residual curatives analyzed by HPLC. Cyclohexanethiol, a decomposition product of CTP, reacted with TBBS producing 2-mercaptobenzothiazole (MBT) and t-butylamine, both of which reacted with CTP. In a polyisoprene compound, the addition of CTP did not delay the formation of the initial crosslinks, however the crosslink density did not increase substantially until the CTP had been consumed. MBT, a product of the crosslinking reaction, reacted preferentially with the CTP and not the TBBS. In the absence of CTP, the MBT was shown to accelerate the rate of TBBS polysulfide formation leading to a rapid rise in crosslink density.

Studies of Polymer-Filler Interaction, Network Structure, Physical Properties, and Fracture of Silica-and Clay-Filled EPDM Rubber in the Presence of a Silane Coupling Agent

1983 ◽  
Vol 56 (4) ◽  
pp. 737-773 ◽  
Author(s):  
P. K. Pal ◽  
S. K. De
Keyword(s):  
Physical Properties ◽  
Network Structure ◽  
Coupling Agent ◽  
Crosslink Density ◽  
Silane Coupling Agent ◽  
Interaction Network ◽  
Epdm Rubber ◽  
Polymer Filler ◽  
Silane Coupling ◽  
Tear Properties

Abstract 1. A silane coupling agent (Si-69) reduces the viscosity and increases the scorch lime in silica- and clay-filled EPDM. The cure lime of silica-filled mixes remained unchanged and that of clay-filled mixes increased on addition of Si-69. 2. In the presence of Si-69, the silica-EPDM system exhibits higher polymer-filler interaction than the clay-EPDM system. 3. Vulcanizates containing Si-69 exhibit higher apparent crosslink density and a higher proportion of polysulfidic crosslinks than the control vulcanizates. 4. Vulcanizates containing Si-69 show improved physical properties. Lower tensile and tear properties in vulcanizates with Si-69 at higher filler loadings is explained via a slippage mechanism. 5. SEM studies of fractured surfaces created under tension, tear, flexing, and abrasion have been made, and changes in the strength of the vulcanizates have been correlated with the fractographs.

The Mechanism of Protection by the Deactivating Effect

1958 ◽  
Vol 31 (4) ◽  
pp. 849-865 ◽  
Author(s):  
Jean le Bras ◽  
Jean-Claude Danjard ◽  
Madeleine Boucher
Keyword(s):  
Chemical Composition ◽  
Network Structure ◽  
Oxidative Degradation ◽  
Antioxidant Effect ◽  
Industrial Practice ◽  
Protective Agents ◽  
Effect Mechanism ◽  
Complex Phenomena ◽  
Crosslinking Agents ◽  
Thermo Oxidative Degradation

Abstract In order to better understand the complex phenomena related to aging, the two following propositions should be considered : (a) Each type of vulcanizate has a particular type of network structure, with characteristics dependent on the number and nature of the crosslinks between the macromolecules. Thermo-oxidative degradation may have varying effects according to the network points which are preferentially attacked. (b) The protection at present employed against the consequences of this degradation is based upon two different mechanisms, i.e., through the antioxidant effect, which retards the scission reaction, or through the deactivating effect, which helps to maintain the network by forming additional crosslinks. If we also take into account the fact that each accelerator is able, as is the deactivator, to create specific new bonds by after-cure, we may suggest an explanation for some unexplained aspects of the related phenomena. From our results and the derived deductions ideas emerge, from which it should be possible to establish, by logic (instead of empirically) and by adaptation to each type of vulcanizate, some rules for the best protection with the present-known protective agents. It should be noted that all preceding observations refer exclusively to the most widely used industrial practice, sulfur curing. However, the knowledge we now have of the deactivating effect mechanism has led us to think that it should also be possible, for vulcanizates produced with other vulcanizing agents, to find substances which will play the same part as our present deactivators, although of a totally different chemical composition. As a matter of fact, the so-called deactivators are but slow-acting crosslinking agents, the new crosslinks resulting from either a mobilization of the unused vulcanizing agent in the vulcanizate or from a direct intervention of the deactivator. We therefore doubt whether their name, derived from the first, and inexact, explanation given for their action, is still justified. However, to change it we should have to evoke an after-crosslinking, a source of confusion with other current terms ; moreover, a number of other wrong terms have been confirmed by use, for instance, the English “antioxidant”. As these deactivators make degradation less active, their original name is perhaps not so inappropriate after all.

Determination of Crosslink Density and Network Structure of NR Vulcanizates by Means of TSSR

2013 ◽  
Vol 844 ◽  
pp. 482-485 ◽  
Author(s):  
Norbert Vennemann ◽  
Christina Schwarze ◽  
Claudia Kummerlöwe
Keyword(s):  
Stress Relaxation ◽  
Natural Rubber ◽  
Network Structure ◽  
Crosslink Density ◽  
Relaxation Spectrum ◽  
Strong Impact ◽  
Relaxation Spectra ◽  
Peak Separation ◽  
Temperature Scanning

Unfilled vulcanizates based on natural rubber (NR) were investigated by temperature scanning stress relaxation (TSSR) measurements. Different sulfur based cure systems, i.e. conventional (CV), semi-efficient (SEV) and efficient (EV) vulcanization system, were used to prepare the vulcanizates. It was found that sulfur/accelerator - ratio has a strong impact on the shape of the relaxation spectrum, deduced from TSSR measurements. By deconvolution of the relaxation spectra, peak separation was performed and 3 different peaks were found in case of CV - cured samples. In contrast, only a single peak was found, in case of the EV-cured sample. After thiolamine treatment the shape of the relaxation spectra altered significantly in case of the CV-cured sample whereas the spectra of the SEV-and EV-cured sample exhibited only slight differences. Additionally, the crosslink density of the samples decreased after thiolamine treatment. This is due to selective cleavage of polysulfidic crosslinks. It has been concluded, that the significant peak in the relaxation spectrum at about 120 °C can be attributed to the cleavage of polysulfidic crosslinks. Furthermore, a linear relationship between the percentage of polysulfidic crosslinks and the sulfur/accelerator - ratio is assumed.

scholarly journals A comparative and experimental study of the reactivity with nitrate radical of two terpenes: <i>α</i>-terpinene and <i>γ</i>-terpinene

2020 ◽  
Vol 20 (23) ◽  
pp. 15167-15189
Author(s):  
Axel Fouqueau ◽  
Manuela Cirtog ◽  
Mathieu Cazaunau ◽  
Edouard Pangui ◽  
Jean-François Doussin ◽  
...  
Keyword(s):  
Main Reaction ◽  
Organic Nitrate ◽  
Organic Nitrates ◽  
Nitrate Radical ◽  
Reaction Products ◽  
Chemical Mechanisms ◽  
Chemical Structures ◽  
Aerosol Mass ◽  
Similar Chemical ◽  
Volatile Organic

Abstract. Biogenic volatile organic compounds (BVOCs) are intensely emitted by forests and crops into the atmosphere. During the night, they react very rapidly with the nitrate radical (NO3), leading to the formation of a variety of functionalized products including organic nitrates and to large amounts of secondary organic aerosols (SOAs). Organic nitrates (ONs) have been shown not only to play a key role in the transport of reactive nitrogen and consequently in the ozone budget but also to be important components of the total organic-aerosol mass, while SOAs are known to play a direct and indirect role in the climate. However, the reactivity of BVOCs with NO3 remains poorly studied. The aim of this work is to provide new kinetic and mechanistic data for two monoterpenes (C10H16), α- and γ-terpinene, through experiments in simulation chambers. These two compounds, which have very similar chemical structures, have been chosen in order not only to overcome the lack of experimental data but also to highlight the influence of the chemical structure on the reactivity. Rate constants have been measured using both relative and absolute methods. They were found to be (1.2±0.5)×10-10 and (2.9±1.1)×10-11 cm3 molecule−1 s−1 for α- and γ-terpinene respectively. Mechanistic studies have also been conducted in order to identify and quantify the main reaction products. Total organic nitrate and SOA yields have been determined. While organic nitrate formation yields appear to be similar, SOA yields exhibit large differences with γ-terpinene being a much more efficient precursor of aerosols. In order to provide explanations for this difference, chemical analysis of the gas-phase products was performed at the molecular scale. Detected products allowed for proposing chemical mechanisms and providing explanations through peroxy and alkoxy reaction pathways.

Observations on the Crosslinking of Natural Rubber with Nitrosophenols and Diisocyanates

1974 ◽  
Vol 47 (1) ◽  
pp. 100-117 ◽  
Author(s):  
F. K. Lautenschlaeger ◽  
M. Myhre
Keyword(s):  
Nitroso Compounds ◽  
Crosslinking Reaction ◽  
Amino Group ◽  
Reaction Products ◽  
Substituted Phenols ◽  
Free Phenol ◽  
Active Intermediates ◽  
Derivatives Of ◽  
Crosslinking Agents ◽  
Sulfur Donor

Abstract 1. The vulcanization system based on nitrosophenols (quinone monoximes) is not primarily based on the formation of a urethane group. Evidence is presented that the crosslink consists of carbon—carbon, carbon—sulfur, and urea groups. Urea groups can be identified in reaction products which also contain the free phenol group of the nitrosophenol (oxime); urethane groups are identified in products which also contain quinone groups. 2. The presence of zinc dithiocarbamate is conducive to the formation of the amino group which is the functional group on which the crosslinking reaction with diisocyanate is based. The dithiocarbamate also acts as a sulfur donor. The dialkyl amino group of the dithiocarbamate is bound into the network. 3. Nitroso compounds which have no tautomeric oxime structures show no vulcanization in combination with free diisocyanate. 4. The level of vulcanization of various substituted phenols, when used in combination with a diisocyanate precursor, is dependent on their thermal decomposition termperatures, but such a dependence is not apparent when these compounds are used in combination with free diisocyanate. 5. A reaction mechanism is suggested for the vulcanization with oximes and diisocyanates which does not require the splitting of their adducts into their components but instead into ionic fragments. This mechanism explains why monoximes lead to vulcanization whereas nitroso compounds do not. 6. Attempts to effect premature vulcanization should be directed towards delaying the formation of the diisocyanate/oxime adduct since it provides the vulcanization-active intermediates. Towards this goal it has been shown that a diisocyanate precursor can be applied but then a thermally stable nitroso compound (oxime) is required. 7. Tautomerism between O-derivatives of oximes, nitrones, and oxaziridines can be assumed to provide a working hypothesis for the discovery of new N-O-containing crosslinking agents for unsaturated polymers.

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