Chemical Structures in CIS-1, 4-Polybutadiene Vulcanizates. Model Compound Approach

1970 ◽  
Vol 43 (3) ◽  
pp. 549-571 ◽  
Author(s):  
E. C. Gregg ◽  
S. E. Katrenick
Keyword(s):  
Molecular Weight ◽  
Calibration Curve ◽  
Model Compound ◽  
Chemical Compounds ◽  
Alkyl Derivative ◽  
Chemical Structures ◽  
Sulfur Vulcanization ◽  
Before And After ◽  
Chemical Crosslinks ◽  
In Cis

Abstract We studied the vulcanization reaction of one curing recipe for cis-1,4-polybutadiene (CB). The curing recipe was zinc oxide (ZnO), diphenylguanidine (DPG), 2,2′-bis(benzothiazolyl) disulfide (MBTS), and sulfur and it produced only polysulfidic crosslinks. Devulcanization of this CB vulcanizate by phenyllithium solution permitted a comparison of the molecular weight of the CB before and after vulcanization. A small but measurable reduction of the molecular weight of the rubber occurred as a result of the vulcanization reaction. Reaction of the curing recipe in cis, cis-1,5-cyclooctadiene (COD) permitted the study of the fate of the curing chemicals in the vulcanizate because COD is an accurate chemical model for CB. This study showed that: 1. The vulcanization reaction consumes none of the DPG and none of the ZnO. 2. An insoluble coating forms on the ZnO and separates it from the vulcanization reaction during at least part of the reaction. 3. All of the MBTS reacts to form one compound: an S-alkyl derivative of 2-mercaptobenzothiazole attached to the rubber molecule at a point next to a thiacyclohexene ring. 4. All the sulfur reacts to form crosslinks and intramolecular rings. The rings are three-, five-, and six-membered thiacycloalkanes and five- and six-membered thiacycloalkenes. Some of the rings are isolated and some are next to crosslinks. 5. The three-membered rings are episulfide and they are very likely the key intermediate to the formation of the cyclic and crosslink structures. 6. The crosslinks are polysulfidic and occur singly and as clusters of two and four. The more crosslinks in a cluster, the less unsaturation in its vicinity. The four-link cluster has no unsaturation and occurs as two pairs with thiacyclopentane rings between. The sum of the single crosslinks and clusters of crosslinks in the model network agrees with the number of elastically effective chemical crosslinks found in the CB vulcanizate as measured by swelling in benzene. The elastically effective chemical crosslinks in the vulcanizate were calculated by the Flory-Rehner equation and the Moore-Watson calibration curve. This agreement proves that the theory of rubber elasticity in the form of the Flory-Rehner equation and the Moore-Watson calibration curve may be used to count the number of elastically effective chemical crosslinks in a sulfur vulcanizate. Three new chemical compounds and a new method for quantitatively titrating mercaptans are disclosed. The success of this technique recommends it for further study of sulfur vulcanization by other recipes and the study of other vulcanizate changes.

Therapeutic Properties of Several Chemical Compounds from Salvia officinalis L. in Alzheimer’s Disease

2020 ◽  
Vol 21 ◽  
Author(s):  
Georgiana Uță ◽  
Denisa Ștefania Manolescu ◽  
Speranța Avram
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Side Effects ◽  
Chemical Compounds ◽  
Natural Compounds ◽  
Salvia Officinalis ◽  
Chemical Structures ◽  
In Silico Studies ◽  
Wide Range ◽  
Salvia Officinalis L

Background.: Currently, the pharmacological management in Alzheimer's disease is based on several chemical structures, represented by acetylcholinesterase and N-methyl-D-aspartate (NMDA) receptor ligands, with still unclear molecular mechanisms, but severe side effects. For this reason, a challenge for Alzheimer's disease treatment remains to identify new drugs with reduced side effects. Recently, the natural compounds, in particular certain chemical compounds identified in the essential oil of peppermint, sage, grapes, sea buckthorn, have increased interest as possible therapeutics. Objectives.: In this paper, we have summarized data from the recent literature, on several chemical compounds extracted from Salvia officinalis L., with therapeutic potential in Alzheimer's disease. Methods.: In addition to the wide range of experimental methods performed in vivo and in vitro, also we presented some in silico studies of medicinal compounds. Results. Through this mini-review, we present the latest information regarding the therapeutic characteristics of natural compounds isolated from Salvia officinalis L. in Alzheimer's disease. Conclusion.: Thus, based on the information presented, we can say that phytotherapy is a reliable therapeutic method in a neurodegenerative disease.

Coactivation of Delayed-Action Vulcanization. Part I. Polymeric, Nonmigratory Cure Coactivators for Accelerated Sulfur Vulcanization

1989 ◽  
Vol 62 (5) ◽  
pp. 957-972
Author(s):  
A. Y. Coran ◽  
F. Ignatz-Hoover ◽  
L. H. Davis
Keyword(s):  
Molecular Weight ◽  
Minimum Loss ◽  
Synthetic Rubber ◽  
Curing Characteristics ◽  
Sulfur Vulcanization ◽  
Delayed Action ◽  
Very High ◽  
Rubber Article

Abstract Rubbery vinylpyridine-butadiene copolymers, containing 20–65% by weight of vinylpyridine monomer units, are effective coactivators of vulcanization for TBBS-accelerated sulfur-vulcanized SBR. In addition to emulsion SBR, the new co-activator has been evaluated in copositions of solution SBR, BR, NR, and various blends. The co-activator is active in all of the compositions which contain butadiene-derived synthetic rubber. This includes blends such as SBR/BR, solution-SBR/BR, SBR/NR, BR/NR, SBR/BR/NR, etc. There is little or no activity in which NR is the only polymer. The most efficacious copolymers contain between 30 and 60% 2-vinylpyridine. The incorporation of such a copolymer into an unvulcanized butadiene-derived rubber mix can give a substantial increase in the rate of crosslink formation with only a minimum loss of scorch resistance. Since the polymeric coactivators are very high in molecular weight, it can be at least tentatively concluded that they will not migrate from one component stock to another in a built-up multi-stock rubber article, either before or during vulcanization. Since the curing characteristics of a vinylpyridine-copolymer-containing TBBS-accelerated stock can be similar to those of TBBS-accelerated NR, it might be concluded that the new additives will solve some of the problems in balancing the cures of adjacent NR and SBR stocks in a multicomponent cured rubber article.

Activators in Accelerated Sulfur Vulcanization

2004 ◽  
Vol 77 (3) ◽  
pp. 512-541 ◽  
Author(s):  
Geert Heideman ◽  
Rabin N. Datta ◽  
Jacques W. M. Noordermeer ◽  
Ben van Baarle
Keyword(s):  
Reaction Mechanisms ◽  
Model Compound ◽  
Background Information ◽  
Zinc Compounds ◽  
Chemical Mechanisms ◽  
Sulfur Vulcanization ◽  
Multifunctional Additives ◽  
Vulcanization Process

Abstract This review provides relevant background information about the vulcanization process, as well as the chemistry of thiuram- and sulfenamide-accelerated sulfur vulcanization with emphasis on the role of activators, to lay a base for further research. It commences with an introduction of sulfur vulcanization and a summary of the reaction mechanisms as described in literature, followed by the role of activators, particularly ZnO. The various possibilities to reduce ZnO levels in rubber compounding, that have been proposed in literature, are reviewed. A totally different approach to reduce ZnO is described in the paragraphs about the various possible roles of multifunctional additives (MFA) in rubber vulcanization. Another paragraph is dedicated to the role of amines in rubber vulcanization, in order to provide some insight in the underlying chemical mechanisms of MFA systems. Furthermore, an overview of Model Compound Vulcanization (MCV) with respect to different models and activator/accelerator systems is given. In the last part of this review, the various functions of ZnO in rubber are summarized. It clearly reveals that the role of ZnO and zinc compounds is very complex and still deserves further clarification.

Olfactory Training Using Heavy and Light Weight Molecule Odors

Perception ◽  
2016 ◽  
Vol 46 (3-4) ◽  
pp. 343-351 ◽  
Author(s):  
Sophia C. Poletti ◽  
Elisabeth Michel ◽  
Thomas Hummel
Keyword(s):  
Molecular Weight ◽  
Olfactory Dysfunction ◽  
Light Weight ◽  
Short Term ◽  
Olfactory Loss ◽  
Short Term Exposure ◽  
Before And After ◽  
Phenyl Ethyl Alcohol ◽  
A Prospective Study ◽  
Olfactory Training

Background Repeated short-term exposure to odors is known to improve olfaction in patients with acquired olfactory dysfunction. The aim was to find out whether differences in molecular weight of odors used for olfactory training influences olfaction. We hypothesized a greater improvement following training with light weight molecule (LWM) odors. Methods A prospective study was performed in patients with posttraumatic (PTOL) and postviral olfactory loss (PVOL). Olfactory training was performed over a period of 5 months. One group ( n = 48) used four odors containing heavy weight molecules (HWM; >150 g/mol) and another ( n = 48) containing LWM (<150 g/mol). Olfaction was tested before and after the training using the Sniffin’ Sticks test. Results Olfactory training was associated with olfactory improvement, with the improvement in PVOL patients being three times greater than that seen in the PTOL group. Compared with LWM training, HWM training was associated with a significantly greater improvement in Phenyl Ethyl Alcohol (PEA) threshold scores in PVOL patients; however, no such improvement could be shown for other subtests or in PTOL patients. Conclusion Overall, training was associated with olfactory improvement. With the exception of threshold scores in PVOL, there were no significant differences between LWM and HWM groups.

Selected chemical compounds in firm and mellow persimmon fruit before and after the drying process

2015 ◽  
Vol 96 (9) ◽  
pp. 3140-3147 ◽  
Author(s):  
Mateja Senica ◽  
Robert Veberic ◽  
Jana Jurhar Grabnar ◽  
Franci Stampar ◽  
Jerneja Jakopic
Keyword(s):  
Chemical Compounds ◽  
Drying Process ◽  
Persimmon Fruit ◽  
Before And After

Vulcanization of Rubber in the Presence of N,N-Diethyl-2-Benzothiazolylsulfenamide as Accelerator

1960 ◽  
Vol 33 (2) ◽  
pp. 361-372 ◽  
Author(s):  
B. A. Dogadkin ◽  
O. N. Beliatskaya ◽  
A. B. Dobromyslova ◽  
M. S. Feldshtein
Keyword(s):  
Induction Period ◽  
Maximum Rate ◽  
Initial Period ◽  
Pure Oxygen ◽  
Butadiene Rubber ◽  
Sulfur Vulcanization ◽  
Analogous Manner ◽  
Chemical Crosslinks ◽  
Main Period ◽  
Kinetics Of

Abstract 1. The vulcanization of rubber in the presence of N,N-diethyl-2-benzothiazolylsulfenamide is characterized by an S-shaped curve for the addition of sulfur with an initial induction period in the reaction. The modulus and number of crosslinks are changed in an analogous manner to the structure of the vulcanizate. 2. The energy of activation of the addition of sulfur in the initial period is equal to 30 kcal per mole as against 14 kcal per mole in the main period. 3. The induction period is increased if the sodium-butadiene rubber is purified from alkali. 4. Molecular oxygen present in the compound being vulcanized decreases the induction period and increases the rate of the addition of the sulfur in the main period. An induction period is not observed when vulcanization is carried out in an atmosphere of pure oxygen. 5. The interaction of N,N-diethyl-2-benzothiazolylsulfenamide with rubber (in the absence of sulfur) at vulcanization temperatures is accompanied by the formation of MBT, diethylamine, and the addition of the elements of the accelerator to the rubber. The kinetics of this process were studied. 6. The interaction of N,N-diethyl-2-benzothiazolyl sulfenamide with rubber leads to the formation of chemical crosslinks between the molecules of rubber (the effect of vulcanization). 7. The change of N,N-diethyl-2-benzothiazolyl sulfenamide under the conditions of normal sulfur vulcanization has the same character as in the interaction of it with rubber. The kinetics of the formation of MBT have a maximum which coincides with the maximum rate of the addition of sulfur to the rubber. 8. A mechanism is presented for the vulcanization and acceleration actions of N,N-diethyl-2-benzothiazolyl sulfenamide which provides for the extraction of hydrogen by the accelerator radicals from the molecular chains of the rubber with the formation of MBT, diethylamine and polymer radicals which are able to interact with the sulfur.

THERMOPHYSICAL AND DYNAMIC PROPERTIES OF BUTADIENE-NITRILE RUBBER FILLED WITH ULTRA HIGH-MOLECULAR WEIGHT POLYETHYLENE

2021 ◽  
Vol 0 (2) ◽  
pp. 36-43
Author(s):  
N.V. Shadrinov ◽  
◽  
A.A. Khristoforova ◽  
Keyword(s):  
Molecular Weight ◽  
Dynamic Properties ◽  
Ultrahigh Molecular Weight Polyethylene ◽  
Physicomechanical Properties ◽  
Butadiene Rubber ◽  
Rubber Compounds ◽  
Ultrahigh Molecular Weight ◽  
Before And After ◽  
Butadiene Nitrile Rubber ◽  
Ultra High Molecular Weight

The results of the study of the complex of properties of an elastomeric composite material based on nitrile butadiene rubber BNKS-18 and ultrahigh molecular weight polyethylene are presented. The effect of UHMWPE on the vulcanization characteristics of rubber compounds, the physicomechanical properties of vulcanizates before and after thermal aging in a hydrocarbon environment and air, and also on the dynamic properties before and after curing are investigated.

Topological characterization of dendrimer, benzenoid, and nanocone

2018 ◽  
Vol 74 (1-2) ◽  
pp. 35-43
Author(s):  
Wei Gao ◽  
Muhammad Kamran Siddiqui ◽  
Najma Abdul Rehman ◽  
Mehwish Hussain Muhammad
Keyword(s):  
Chemical Properties ◽  
Chemical Compounds ◽  
Topological Indices ◽  
Zagreb Index ◽  
Topological Characterization ◽  
Complex Molecules ◽  
Chemical Structures ◽  
Physico Chemical ◽  
Quantitative Structure Activity Relationships

Abstract Dendrimers are large and complex molecules with very well defined chemical structures. More importantly, dendrimers are highly branched organic macromolecules with successive layers or generations of branch units surrounding a central core. Topological indices are numbers associated with molecular graphs for the purpose of allowing quantitative structure-activity relationships. These topological indices correlate certain physico-chemical properties such as the boiling point, stability, strain energy, and others, of chemical compounds. In this article, we determine hyper-Zagreb index, first multiple Zagreb index, second multiple Zagreb index, and Zagreb polynomials for hetrofunctional dendrimers, triangular benzenoids, and nanocones.

scholarly journals Average molecular weight of surfactants in aerosols

2007 ◽  
Vol 7 (5) ◽  
pp. 13805-13838 ◽  
Author(s):  
M. T. Latif ◽  
P. Brimblecombe
Keyword(s):  
Molecular Weight ◽  
Surface Tension ◽  
Atmospheric Aerosols ◽  
Average Molecular Weight ◽  
Molecular Size ◽  
Weight Fraction ◽  
Ozone Exposure ◽  
Before And After ◽  
Fine Mode ◽  
Active Substances

Abstract. Surfactants in atmospheric aerosols determined as methylene blue active substances (MBAS) and ethyl violet active substances (EVAS). The MBAS and EVAS concentrations can be correlated with surface tension as determined by pendant drop analysis. The effect of surface tension was more clearly indicated in fine mode aerosol extracts. The concentration of MBAS and EVAS was determined before and after ultrafiltration analysis using AMICON centrifuge tubes that define a 5000 Da (5 K Da) nominal molecular weight fraction. Overall, MBAS and to a greater extent EVAS predominates in fraction with molecular weight below 5 K Da. In case of aerosols collected in Malaysia the higher molecular fractions tended to be a more predominant. The MBAS and EVAS are correlated with yellow to brown colours in aerosol extracts. Further experiments showed possible sources of surfactants (e.g. petrol soot, diesel soot) in atmospheric aerosols to yield material having molecular size below 5 K Da except for humic acid. The concentration of surfactants from these sources increased after ozone exposure and for humic acids it also general included smaller molecular weight surfactants.

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