Degradation of Rubber by Chemical Agents in Solution

1961 ◽  
Vol 34 (4) ◽  
pp. 1212-1219
Author(s):  
G. H. Foxley
Keyword(s):  
Free Radicals ◽  
Low Temperatures ◽  
Model Compound ◽  
Polymer Degradation ◽  
Chain Scission ◽  
Redox Systems ◽  
Chemical Agents ◽  
The Subject ◽  
Partial Fulfillment

Abstract It is clear that the subject of polymer degradation by chemical agents is an active branch of polymer chemistry. This is reflected in the large number of patents applying to polymer degradation and no attempt has been made to include every appropriate patent. Much of the comparative work is based on equal weights, rather than equal numbers of molecules, so that the true comparisons of the efficiency of peptizers are often difficult. It has been shown that polymer degradation can proceed via several mechanisms all of which involve free radicals and the main points can be summarized as follows :— In solutions at low temperatures the initiatory free radicals come from the added peptizer such as benzoyl peroxide or bis-azoisobutyronitrile. Although oxygen accelerates the reaction, it is not essential, and there is appreciable degradation in the absence of oxygen. Thiols are active only when oxygen is present even at high temperature. This is somewhat surprising, since the rubber radicals produced by thermal scission should be just as active as those produced by mastication and be capable of reaction with thiols, and serves to emphasize the importance of the role of oxygen in peptization by thiols and disulfides. Oxygen is also necessary for degradation by redox systems and in its absence structurizing takes place. The lack of work on triphenyl methane derivatives is somewhat surprising in view of the ease with which they undergo homolysis to give free radicals. However, it is not sufficient to introduce any type of free radical and expect degradation: stabilized free radicals are the best peptizers, unstable radicals can add to olefinic bonds and cause crosslinking rather than chain scission. Squalene has been used as a model compound for the study of the reactions of natural rubber with free radicals in a similar manner to the use of methylcyclohexene as a model compound for oxidation studies. This review forms part of a dissertation submitted in partial fulfillment of the requirements for the London University M.Sc. (External) Examination.

Mechanical Chain-Scission in Rubber Vulcanizate at Low Temperatures

1979 ◽  
Vol 52 (4) ◽  
pp. 773-780 ◽  
Author(s):  
T. Kusano ◽  
K. Kobayashl ◽  
K. Murakami
Keyword(s):  
Free Radicals ◽  
Chain Length ◽  
Low Temperatures ◽  
Crosslink Density ◽  
Glassy State ◽  
Chain Scission ◽  
Molecular Chain ◽  
Yield Strain ◽  
Air Stream ◽  
Intermolecular Reaction

Abstract When vulcanized natural rubbers are forced to extend in the glassy state, free radicals are produced by the scission of the primary chain. The amount of the free radicals increases with the strain. The tensile yield strain decreases with the decrease of the molecular chain length between crosslinks. This behavior is explainable on the basis of the limited chain extensibility. The extended chains are broken with further increases of the strain. The mechanically produced free radicals are quite stable below about −40°C. The crosslink density of the chain-ruptured material increases about 2∼3×10−5 mol/cm3. This fact shows that the free radicals are consumed not only by recombination but by the intermolecular reaction. In both sulfur and DCP vulcanizates, the network chains rather than the crosslinks are broken by stretching. In an air stream, some free radicals react with oxygen and others form crosslinks.

Redox Systems in the Initiation of Radical Processes. Mechanism of Action

1959 ◽  
Vol 32 (1) ◽  
pp. 244-256
Author(s):  
B. A. Dolgoplosk ◽  
E. I. Tinyakova
Keyword(s):  
Free Radicals ◽  
Mechanism Of Action ◽  
Low Temperatures ◽  
Oxidation States ◽  
Reversible Systems ◽  
Redox Systems ◽  
The Third ◽  
Destructive Processes ◽  
Radical Processes ◽  
Variable Valency

Abstract The following redox systems capable of initiating radical polymerizations are discussed: (1) Systems of the first type, where the reaction leads to the formation of a single radical: (a) Mechanism of action of reversible systems involving dienols and salts of metals of variable valency. (b) Mechanism of the decomposition of hydroperoxides by the action of salts of metals of variable valency in their higher oxidation states. (2) Systems of the second type, where the reaction leads to the formation of two radicals. Mechanism of action and effectiveness of systems involving hydroperoxides, quinol, and sulfite. (3) Systems of the third type, in which the formation of free radicals is not directly linked to the redox process. Mechanism of action of systems involving diazoamino compounds and “polyamine” systems. (4) Crosslinking of unsaturated polymers at low temperatures by the action of redox systems. Transition from crosslinking to destructive processes in presence of oxygen.

scholarly journals Szabad gyökök és a máj ischaemiás-reperfúziós károsodása

2015 ◽  
Vol 156 (47) ◽  
pp. 1904-1907 ◽  
Author(s):  
Attila Szijártó
Keyword(s):  
Free Radicals ◽  
Organ Damage ◽  
Systemic Reactions ◽  
Chemical Agents ◽  
Pathophysiological Role ◽  
Polymerase Inhibitor ◽  
Current Article ◽  
Clinical Conditions

The critical importance of the ischemic-reperfusive injury is well documented with regards to numerous organs and clinical conditions. Oxygen free radicals play a central role in the mediation of the injury, which dominantly influences the prevalence of postoperative complications, (long term) organ damage, and the potential manifestation of systemic reactions. The both anatomically and pathophysiologically unique ischemic-reperfusive injury of the liver, which is expressively vulnerable to free radicals, is of utmost importance in liver surgery. Several techniques (adaptive maneuvers, chemical agents) are known to ameliorate the reperfusive injury. Based on the prior research of the workgroup of the author, the aim of the current article is to overview the set of measures capable of attenuating ischemic-reperfusive injury (ischemic preconditioning, -perconditioning, administration of adenosine, -inosine, -levosimendan, and -poly-ADP-ribose-polymerase inhibitor), with special attention to the ischemic-reperfusive injury of the liver, as well as the special pathophysiological role of free radicals in mediating hepatic damage. Orv. Hetil., 2015, 156(47), 1904–1907.

Point and planar defects in the iron sulfide compounds Fe1-xS

1984 ◽  
Vol 42 ◽  
pp. 434-435
Author(s):  
Thao A. Nguyen
Keyword(s):  
Low Temperatures ◽  
Direct Evidence ◽  
Iron Sulfide ◽  
Planar Defects ◽  
Selective Area ◽  
Vacancy Ordering ◽  
Different Types ◽  
Lattice Images ◽  
The Subject ◽  
Beam Lattice

It is well known that the large deviations from stoichiometry in iron sulfide compounds, Fe1-xS (0≤x≤0.125), are accommodated by iron vacancies which order and form superstructures at low temperatures. Although the ordering of the iron vacancies has been well established, the modes of vacancy ordering, hence superstructures, as a function of composition and temperature are still the subject of much controversy. This investigation gives direct evidence from many-beam lattice images of Fe1-xS that the 4C superstructure transforms into the 3C superstructure (Fig. 1) rather than the MC phase as previously suggested. Also observed are an intrinsic stacking fault in the sulfur sublattice and two different types of vacancy-ordering antiphase boundaries. Evidence from selective area optical diffractograms suggests that these planar defects complicate the diffraction pattern greatly.

Top-Down Processing and Visual Reorientation Illusions in a Virtual Reality Environment

2004 ◽  
Vol 63 (3) ◽  
pp. 143-149 ◽  
Author(s):  
Fred W. Mast ◽  
Charles M. Oman
Keyword(s):  
Virtual Reality ◽  
Visual Processing ◽  
Line Length ◽  
Perceptual Cues ◽  
Virtual Reality Environment ◽  
Top Down ◽  
Test Conditions ◽  
The Subject ◽  
Processing Mechanisms

The role of top-down processing on the horizontal-vertical line length illusion was examined by means of an ambiguous room with dual visual verticals. In one of the test conditions, the subjects were cued to one of the two verticals and were instructed to cognitively reassign the apparent vertical to the cued orientation. When they have mentally adjusted their perception, two lines in a plus sign configuration appeared and the subjects had to evaluate which line was longer. The results showed that the line length appeared longer when it was aligned with the direction of the vertical currently perceived by the subject. This study provides a demonstration that top-down processing influences lower level visual processing mechanisms. In another test condition, the subjects had all perceptual cues available and the influence was even stronger.

The future role of the psychiatrist in Europe – a UEMS perspective

2014 ◽  
Vol 11 (01) ◽  
pp. 35-42
Author(s):  
M. Hermans
Keyword(s):  
Mental Health ◽  
Mental Health Professionals ◽  
Health Professionals ◽  
General Interest ◽  
Future Role ◽  
Personal Opinion ◽  
The Future ◽  
The Subject ◽  
The Many

SummaryThe author presents his personal opinion inviting to discussion on the possible future role of psychiatrists. His view is based upon the many contacts with psychiatrists all over Europe, academicians and everyday professionals, as well as the familiarity with the literature. The list of papers referred to is based upon (1) the general interest concerning the subject when representing ideas also worded elsewhere, (2) the accessibility to psychiatrists and mental health professionals in Germany, (3) being costless downloadable for non-subscribers and (4) for some geographic aspects (e.g. Belgium, Spain, Sweden) and the latest scientific issues, addressing some authors directly.

Alignment

2016 ◽  
pp. 33-50
Author(s):  
Pier Giuseppe Rossi
Keyword(s):  
Teaching And Learning ◽  
Enactive Approach ◽  
The World ◽  
Strategic Role ◽  
Education Today ◽  
Current Context ◽  
The Subject

The subject of alignment is not new to the world of education. Today however, it has come to mean different things and to have a heuristic value in education according to research in different areas, not least for neuroscience, and to attention to skills and to the alternation framework.This paper, after looking at the classic references that already attributed an important role to alignment in education processes, looks at the strategic role of alignment in the current context, outlining the shared construction processes and focusing on some of the ways in which this is put into effect.Alignment is part of a participatory, enactive approach that gives a central role to the interaction between teaching and learning, avoiding the limits of behaviourism, which has a greater bias towards teaching, and cognitivism/constructivism, which focus their attention on learning and in any case, on that which separates a teacher preparing the environment and a student working in it.

The Role of the Initiator System in the Synthesis of Acidic Multifunctional Nanoparticles Designed for Molecular Imprinting of Proteins

2020 ◽  
Vol 65 (1) ◽  
pp. 28-41
Author(s):  
Marwa Aly Ahmed ◽  
Júlia Erdőssy ◽  
Viola Horváth
Keyword(s):  
Acrylic Acid ◽  
Binding Affinity ◽  
Molecular Imprinting ◽  
Low Temperatures ◽  
Ammonium Persulfate ◽  
Sodium Bisulfite ◽  
Multifunctional Nanoparticles ◽  
High Affinity ◽  
Initiator System

Multifunctional nanoparticles have been shown earlier to bind certain proteins with high affinity and the binding affinity could be enhanced by molecular imprinting of the target protein. In this work different initiator systems were used and compared during the synthesis of poly (N-isopropylacrylamide-co-acrylic acid-co-N-tert-butylacrylamide) nanoparticles with respect to their future applicability in molecular imprinting of lysozyme. The decomposition of ammonium persulfate initiator was initiated either thermally at 60 °C or by using redox activators, namely tetramethylethylenediamine or sodium bisulfite at low temperatures. Morphology differences in the resulting nanoparticles have been revealed using scanning electron microscopy and dynamic light scattering. During polymerization the conversion of each monomer was followed in time. Striking differences were demonstrated in the incorporation rate of acrylic acid between the tetramethylethylenediamine catalyzed initiation and the other systems. This led to a completely different nanoparticle microstructure the consequence of which was the distinctly lower lysozyme binding affinity. On the contrary, the use of sodium bisulfite activation resulted in similar nanoparticle structural homogeneity and protein binding affinity as the thermal initiation.

TheOrvosi Hetilap (Hungarian Medical Journal)in the network of medical journals

2014 ◽  
Vol 155 (22) ◽  
pp. 876-879
Author(s):  
András Schubert
Keyword(s):  
Medical Journal ◽  
Scientific Knowledge ◽  
Knowledge Network ◽  
Scientific Journals ◽  
Scientific Enterprise ◽  
Medical Journals ◽  
The Subject

The role of networks is swiftly increasing in the production and communication of scientific knowledge. Network aspects have, therefore, an ever growing importance in the analysis of the scientific enterprise, as well. The present paper demonstrates some techniques of studying the network of scientific journals on the subject of seeking the position of Orvosi Hetilap (Hungarian Medical Journal) in the international journal network. Orv. Hetil., 2014, 155(22), 876–879.

The Impact of Quantitative Easing on Emerging Markets – Literature Review

e-Finanse ◽  
2018 ◽  
Vol 14 (4) ◽  
pp. 67-76
Author(s):  
Piotr Bartkiewicz
Keyword(s):  
Emerging Markets ◽  
Large Scale ◽  
Empirical Literature ◽  
Quantitative Easing ◽  
Methodological Choices ◽  
The Subject ◽  
Methodological Approaches ◽  
The Impact ◽  
Sufficient Precision

AbstractThe article presents the results of the review of the empirical literature regarding the impact of quantitative easing (QE) on emerging markets (EMs). The subject is of interest to policymakers and researchers due to the increasingly larger role of EMs in the world economy and the large-scale capital flows occurring after 2009. The review is conducted in a systematic manner and takes into consideration different methodological choices, samples and measurement issues. The paper puts the summarized results in the context of transmission channels identified in the literature. There are few distinct methodological approaches present in the literature. While there is a consensus regarding the direction of the impact of QE on EMs, its size and durability have not yet been assessed with sufficient precision. In addition, there are clear gaps in the empirical findings, not least related to relative underrepresentation of the CEE region (in particular, Poland).

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