Studies in polymerization XIV. The Photosensitized initiation of vinyl polymerization by the carbonyls of group VII metals

1966 ◽  
Vol 292 (1429) ◽  
pp. 153-167 ◽  
Keyword(s):  
Free Radicals ◽  
Carbon Tetrachloride ◽  
The Other ◽  
Metal Carbonyls ◽  
Dark Reaction ◽  
Vinyl Polymerization ◽  
Rate Of Polymerization ◽  
Rhenium Carbonyl ◽  
New Feature ◽  
Manganese Carbonyl

The photoinitiation of vinyl polymerization, sensitized by rhenium carbonyl in the presence of carbon tetrachloride, has been studied at A = 3650 Å. Although in some ways the course of reaction is similar to that observed with manganese carbonyl as photosensitizer (Bamford, Crowe & Wayne 1965 a ), yet one important new feature is found with rhenium carbonyl. After irradiation a relatively high ‘dark’ rate of polymerization persists for several hours, and leads ultimately to high conversions. Studies made to elucidate the mechanism of the dark reaction are presented in this paper. It is shown that the kinetic results are consistent with the formation of two photolytic fragments, only one of which reacts rapidly with carbon tetrachloride to generate free radicals; the other reacts more slowly, so that its concentration builds up gradually during irradiation and decays over several hours after the light has been turned off. The quantum yield for initiation in the light is only slightly greater than unity, the result expected if the second fragment reacts but slowly with carbon tetrachloride. A comparison of the initiation photosensitized by manganese and rhenium carbonyls makes possible certain generalizations about the photochemistry of the group VII metal carbonyls, and suggestions are made about the primary and secondary photolytic processes in these systems.

Studies in polymerization - XV. The photosensitized initiation of vinyl polymerization by manganese carbonyl

1965 ◽  
Vol 284 (1399) ◽  
pp. 455-468 ◽  
Keyword(s):  
Carbon Tetrachloride ◽  
Quantum Yield ◽  
Methyl Methacrylate ◽  
Kinetic Study ◽  
Chemical Nature ◽  
Reaction Scheme ◽  
Low Concentration ◽  
Vinyl Polymerization ◽  
Manganese Carbonyl ◽  
Kinetic Features

It has been found that a system consisting of manganese carbonyl and a low concentration of carbon tetrachloride can act as an efficient photoinitiator of vinyl polymerization. This paper describes a kinetic study of the mechanism of photoinitiation at λ = 4358 Å, in which methyl methacrylate was the monomer. Trichloromethyl radicals are shown to be the initiating species. The main observations are consistent with a reaction scheme in which a primary product F of the photolysis of the carbonyl forms an adduct with carbon tetrachloride. This adduct may either dissociate into trichloromethyl radicals or be destroyed by reaction with F . Suggestions are made as to the chemical nature of F . Other mechanisms are considered which explain certain of the kinetic features observed. The quantum yield of photoinitiation is a function of [CCl 4 ]/ I abs and rises monotonically with a limit of unity.

Initiation of Vinyl Polymerization by Manganese Carbonyl and Carbon Tetrachloride

Nature ◽  
1967 ◽  
Vol 215 (5102) ◽  
pp. 699-701 ◽  
Author(s):  
L. I. B. HAINES ◽  
A. J. POË
Keyword(s):  
Carbon Tetrachloride ◽  
Vinyl Polymerization ◽  
Manganese Carbonyl

The effect of cation concentration on the nitrogen splitting constant of nitroxide free radicals

1990 ◽  
Vol 55 (10) ◽  
pp. 2377-2380
Author(s):  
Hamza A. Hussain
Keyword(s):  
Hydrogen Peroxide ◽  
Hydrogen Bonding ◽  
Free Radicals ◽  
Esr Spectroscopy ◽  
The Other ◽  
Tetraethylammonium Bromide ◽  
Splitting Constant ◽  
The One ◽  
Positively Charged ◽  
Two Equilibria

Nitroxide free radicals prepared from diethylamine, piperidine and pyrrolidine by oxidation with hydrogen peroxide were studied by ESR spectroscopy. The changes in the 14N splitting constant (aN) caused by the addition of KBr or tetraethylammonium bromide were measured in dependence on the concentration of the ions. For diethylamine nitroxide and piperidine nitroxide, the results are discussed in terms of two equilibria: the one, involving the anion, is associated with a gain or loss of hydrogen bonds to the nitroxide oxygen atom, the other is associated with the formation of solvent shared units involving the cation, which results in changes in the hydrogen bonding strenght. The large increase in the aN value in the case of pyrrolidine nitroxide is explained in terms of an interaction from one side of the positively charged N atom; the increase in aN in the case of diethylamine and piperidine nitroxides is explained in terms of interactions with both sides of the positively charged N atom.

THE ISOPIESTIC METHOD APPLIED TO SORPTION ISOTHERMS

1949 ◽  
Vol 27b (2) ◽  
pp. 87-100 ◽  
Author(s):  
S. Barnartt ◽  
J. B. Ferguson
Keyword(s):  
Carbon Tetrachloride ◽  
Linear Relation ◽  
Sorption Isotherms ◽  
Sorption Process ◽  
The Other ◽  
Isopiestic Method ◽  
Simple Criterion ◽  
Water Vapors ◽  
Linear Sections ◽  
Wide Pressure

The isopiestic method has been applied to the sorption of carbon tetrachloride and water vapors by activated coconut shell charcoals. The isopiestic charges were found to be linearly related over wide pressure ranges. Isotherms formed by plotting the isopiestic charges of two charcoals one against the other consisted of three linear sections for both carbon tetrachloride and water. If the pressure isotherm of one charcoal be known, those of other charcoals may be computed from it by weighing relatively few isopiestic charges. Errors inherent in the measurement of equilibrium pressures, as well as those caused by the drift of the pressure isotherms towards higher sorption capacities at a given pressure, are eliminated in the isopiestic method of comparing charcoals. The linear relation between the isopiestic charges affords a simple criterion of rejection for equations proposed to fit the pressure isotherms. It also throws into relief the structural regularities in activated charcoals. The existence of discontinuities m the sorption process, reported by previous experimenters, is supported by the isopiestic data.

Mastication of Rubber. II. Interpolymerization of Natural Rubber and Neoprene on Cold Milling

1956 ◽  
Vol 29 (2) ◽  
pp. 427-437
Author(s):  
D. J. Angier ◽  
W. F. Watson
Keyword(s):  
Free Radicals ◽  
Natural Rubber ◽  
Small Molecules ◽  
The Other ◽  
Polymer Molecules ◽  
Commercially Important ◽  
The Individual ◽  
Cold Mill ◽  
General Method ◽  
Butadiene Styrene

Abstract The softening of elastomers on cold milling results from scission of the polymer molecules by the applied shearing forces. The ruptured chains are free radicals, which can undergo mutual combination, interaction with oxygen and various additives, and branching (grafting) on to other polymer molecules. A general method of producing graft and block interpolymers between elstomers is therefore indicated, namely, to cold-mill the polymers together in the absence of small molecules which can terminate the polymeric radicals in order that the radicals may cross-terminate or graft onto the polymer molecules of the other type. A survey of several pairs of the commercially important elastomers, natural rubber, butadiene-styrene, Neoprene, and butadiene-acrylonitrile, has shown that cold milling does effect interlinking. Detailed results for the rubber-Neoprene system are reported in this communication. Experimental verification of polymer interlinking was obtained from the solubility properties of the milled elastomers. Cold milling of Neoprene under nitrogen produces gel, whereas of natural rubber does not, but the milling of mixtures gives gels containing natural rubber. Also, the solubilities and precipitation of the milled mixtures cannot be accounted for by these properties of the individual polymers. Finally, Neoprene-natural rubber mixtures, after and not before cold-milling, can be cross-linked by magnesium oxide, with rubber bound into the vulcanizate.

Studies in polymerization. XIII. The activated initiation of vinyl polymerization by metal carbonyls

1962 ◽  
Vol 268 (1335) ◽  
pp. 553-566 ◽  
Keyword(s):  
Kinetic Mechanism ◽  
Molybdenum Hexacarbonyl ◽  
Metal Carbonyls ◽  
Group Vi ◽  
Radical Intermediates ◽  
Vinyl Polymerization ◽  
Organic Halogen ◽  
Halogen Compounds ◽  
Iodine Compounds ◽  
Reaction Proceeds

It has been found that the hexaearbonyls of group VI metals in the presence of some organic halogen compounds are active initiators of vinyl polymerization. Molybdenum hexacarbonyl is the most active, and halogen compounds containing —CC1 3 , —CBr 3 are generally more effective than those with fewer halogen atoms joined to a single carbon. Fluorine and iodine compounds are inactive. A study has been made of the initiation of the polymerization of methyl methacrylate by the Cr(CO) 6 + CCl 4 system. The polymerization is markedly retarded by carbon monoxide. It is shown that the reaction proceeds through free-radical intermediates, and a kinetic mechanism for initiation is derived (equation (4)) leading to the expression (5) for the rate of chain starting. This quantity may be calculated from (5) with the aid of the numerical values in table 3. Kinetic observations are in satisfactory agreement with this mechanism. The nature of the participating reactions is discussed.

Comparative Evaluation of Onion Germplasm (Allium Cepa L.) Of Bangladesh for Physical And Antioxidant Properties

2021 ◽  
Vol 19 (1) ◽  
pp. 113-123
Author(s):  
PK Dash ◽  
S Das ◽  
MA Mannan ◽  
M Jahan
Keyword(s):  
Free Radicals ◽  
Antioxidant Properties ◽  
Biological Properties ◽  
Physicochemical Analysis ◽  
The Other ◽  
Antioxidant Compounds ◽  
Visual Methods ◽  
Ic50 Value ◽  
Onion Germplasm

Determination of antioxidant activity is one of the key elements for understanding the biological properties of a widely used spice onion (A. cepa). In contrast, physical properties help understand the textural quality of onion necessary for postharvest operations of sorting and grading in particular. Considering the physicochemical importance of onion, the present study focused on the determination of physical attributes and antioxidant content of the onion germplasm in Bangladesh using visual methods and 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay, respectively. The five-onion germplasms (BARI Piaz-2, BARI Piaz-3, BARI Piaz-4, BARI Piaz-5, Faridpuri Vati) collected from selected onion growers of the Department of Agricultural Extension (DAE) of the southwestern part of Bangladesh were used as treatments for physicochemical analysis at the Horticulture laboratory of the Agrotechnology Discipline, Khulna University, Khulna, Bangladesh during the period from February to August 2019. The laboratory study was laid out in Completely Randomized Design (CRD) with three replications. Most of the physical characteristics of onion were highest in germplasm-1 than those of the other germplasm tested. The results showed that the DPPH free radicals were scavenged by all onion germplasm extracts in a concentration-dependent pattern. The highest IC50 value (238.10 ppm) was noticed in germplasm-3 and the lowest in germplasm-5 (161.29 ppm) with no statistical difference from germplasm-4 (172.41 ppm). The lower IC50 value indicating that onion germplasms-5 and -4 extracts were more potent in scavenging free radicals than the other onion germplasms. Thus, the low IC50 value facilitated the germplasm-5 and -4 to be enriched with antioxidant compounds significantly in higher amounts than the others. SAARC J. Agric., 19(1): 113-123 (2021)

scholarly journals Unidentified emission features in the R Coronae Borealis star V854 Centauri

2018 ◽  
Vol 610 ◽  
pp. L6 ◽  
Author(s):  
L. C. Oostrum ◽  
B. B. Ochsendorf ◽  
L. Kaper ◽  
A. G. G. M. Tielens
Keyword(s):  
Near Infrared ◽  
Physical Nature ◽  
The Other ◽  
Large Telescope ◽  
Circumstellar Material ◽  
Spatially Resolved ◽  
Broad Emission ◽  
Very Large Telescope ◽  
New Feature ◽  
Molecular Nature

During its 2012 decline, the R Coronae Borealis star (RCB) V854 Cen was spectroscopically monitored with X-shooter on the ESO Very Large Telescope. The obscured optical and near-infrared spectrum exhibits many narrow and several broad emission features, as previously observed. The envelope is spatially resolved along the slit and allows for a detailed study of the circumstellar material. In this Letter, we report on the properties of a number of unidentified visual emission features (UFs), including the detection of a new feature at 8692 Å. These UFs have been observed in the Red Rectangle (RR), but their chemical and physical nature is still a mystery. The previously known UFs behave similarly in the RR and in V854 Cen, but are not detected in six other observed RCBs. Some hydrogen might be required for the formation of their carrier(s). The λ8692 UF is present in all RCBs. Its carrier is likely of a carbonaceous molecular nature, presumably different from that of the other UFs.

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