The Kinetics of Polymerization Reactions

1945 ◽  
Vol 18 (2) ◽  
pp. 223-235 ◽  
Author(s):  
G. Gee ◽  
H. W. Melville
Keyword(s):  
Half Life ◽  
Molecular Size ◽  
The Other ◽  
Chain Growth ◽  
Extreme Conditions ◽  
Kinetics Of Polymerization ◽  
Molecular Sizes ◽  
Mathematical Difficulties ◽  
The One ◽  
Kinetics Of

Abstract A general treatment of the kinetics of polymerization reactions is given to cover the two extreme conditions in which the lifetime of chain growth is (1) small, and (2) large compared with the half life of the monomer. Case (1) is considered on the basis of the assumption that the velocity coefficients do not depend on molecular size. Case (2) is considered for propagation coefficients which are on the one hand independent, and on the other hand dependent on molecular size. In addition, the distribution of molecular sizes is computed in those cases where the mathematical difficulties are not insurmountable. The application of these results to the analysis of polymerization reactions is discussed. The work described in this paper was completed when war broke out, and was to have been published as part of a book on polymerization processes. In view of the interest and development in these matters, it was felt desirable to give this account of these ideas now.

scholarly journals Adipo-Myokines: Two Sides of the Same Coin—Mediators of Inflammation and Mediators of Exercise

2013 ◽  
Vol 2013 ◽  
pp. 1-16 ◽  
Author(s):  
Silja Raschke ◽  
Jürgen Eckel
Keyword(s):  
Skeletal Muscle ◽  
Mrna Level ◽  
Cell Types ◽  
The Other ◽  
Target Tissue ◽  
Beneficial Effects ◽  
Mediators Of Inflammation ◽  
The One ◽  
Two Sides ◽  
Kinetics Of

This review summarizes the current literature regarding the most discussed contraction-regulated moykines like IL-6, IL-15, irisin, BDNF, ANGPTL4, FGF21, myonectin and MCP-1. It is suggested that the term myokine is restricted to proteins secreted from skeletal muscle cells, excluding proteins that are secreted by other cell types in skeletal muscle tissue and excluding proteins which are only described on the mRNA level. Interestingly, many of the contraction-regulated myokines described in the literature are additionally known to be secreted by adipocytes. We termed these proteins adipo-myokines. Within this review, we try to elaborate on the question why pro-inflammatory adipokines on the one hand are upregulated in the obese state, and have beneficial effects after exercise on the other hand. Both, adipokines and myokines do have autocrine effects within their corresponding tissues. In addition, they are involved in an endocrine crosstalk with other tissues. Depending on the extent and the kinetics of adipo-myokines in serum, these molecules seem to have a beneficial or an adverse effect on the target tissue.

Ozonation of bromide-containing drinking waters:a delicate balance between disinfection and bromate formation

2000 ◽  
Vol 41 (7) ◽  
pp. 53-59 ◽  
Author(s):  
U. von Gunten ◽  
U. Pinkernell
Keyword(s):  
Temperature Dependence ◽  
Low Temperatures ◽  
The Other ◽  
Ozone Exposure ◽  
Oh Radicals ◽  
Strong Temperature Dependence ◽  
Control Options ◽  
The One ◽  
Kinetics Of ◽  
Ozonation Process

The occurrence of Cryptosporidium in raw waters and bromate formation during ozonation of bromide-containing waters leads to a difficult optimisation of ozonation processes. On the one hand inactivation of Cryptosporidium requires high ozone exposures, on the other hand under these conditions bromate formation is favored. In order to overcome this problem we need information about (i) the oxidant concentrations (ozone and OH radicals) during an ozonation process, (ii) kinetics of the inactivation of Cryptosporidium, (iii) kinetics and mechanism of bromate formation, and (iv) the reactor hydraulics. The strong temperature dependence of the inactivation of Cryptosporidium which results in a higher ozone exposure (time-integrated action of ozone) at low temperatures makes it more difficult to fulfil disinfection and bromate standards at low temperatures. Underthese conditions control options for bromate formation can be applied. Depressionof pH and addition of ammonia have been selected to be the best options. For a given ozone exposure both measures lead to a reduction of bromate formation in the order of 50%.

Effect of the structure of alkyllithium on the polymerization kinetics of isoprene

1984 ◽  
Vol 49 (10) ◽  
pp. 2269-2274 ◽  
Author(s):  
U. D. N. Bajpai ◽  
Miroslav Kašpar ◽  
Jiří Trekoval
Keyword(s):  
Induction Period ◽  
Polymerization Kinetics ◽  
The Other ◽  
Kinetics Of Polymerization ◽  
Reaction Orders ◽  
Kinetics Of

The kinetics of polymerization of isoprene in benzene initiated with ethyl-, propyl-, butyl-, hexyl-, octyl-, 2-butyl-, 3-hexyl-, 2-octyl-, and 6-methylheptyllithium was investigated. With the exception of ethyllithium , a distinct initial induction period decreasing steeply with increasing concentration of the initiator was observed for all n-alkyllithium initiators. No induction period was observed with the other initiators. The reaction orders decreased at the highest concentrations for most of the initiators, sometimes even to negative values. In the case of ethyl-, 2-butyl- and octyl-lithium this phenomenon has not been observed in the range investigated.

scholarly journals Editorial

2005 ◽  
Vol 4 (1) ◽  
pp. 1-2 ◽  
Author(s):  
Anja C. Anderson ◽  
Axel Brandenburg
Keyword(s):  
Solar System ◽  
Artificial Life ◽  
The Other ◽  
Extreme Conditions ◽  
The Public ◽  
The World ◽  
Earth Like Planets ◽  
The One ◽  
Astronomy And Astrophysics ◽  
Broad Interest

Astrobiology harbours a number of rather diverse disciplines combining expertise in astronomy and astrophysics, biophysics and biology, chemistry and biochemistry, geophysics and geology, as well as mathematics. The need to foster advances in astrobiology are two-fold. On the one hand, there are many scientific reasons: the discoveries of extra-solar planets which contribute to our understanding of the Solar System and the formation of Earth-like planets, the realization that life can thrive under rather extreme conditions making it more probable for life to exist elsewhere in the Solar System and beyond, and the fact that major resources are being spent in developing the technology to produce artificial life, which helps us to appreciate the range of possibilities that nature may have utilized on Earth or elsewhere. On the other hand, astrobiology touches upon some fundamental questions regarding our very existence, and it is perhaps this that attracts the broad interest of scientists and the public alike. As a result, astrobiology networks and astrobiology centres have been emerging all over the world.

Emulsion Polymerization of Methyl Methacrylate and Butyl Acrylate Using Non-Ionic Polyurethane as Emulsifier

2013 ◽  
Vol 842 ◽  
pp. 70-73
Author(s):  
Jie Zheng ◽  
Guo Hao Xie ◽  
Xin Hu ◽  
Huan An Peng
Keyword(s):  
Surfactant Concentration ◽  
Initial Period ◽  
High Rate ◽  
Latex Film ◽  
Low Molecular Weight ◽  
Kinetics Of Polymerization ◽  
Good Surface ◽  
The One ◽  
Kinetics Of ◽  
Better Than

In this paper, non-ionic polyurethane surfactant which has real good surface activity and better emulsifying capability was totally substitute low molecular weight surfactant for preparing polyacrylate emulsion without any other stabilizer. Kinetics of polymerization was studied and the results showed polymerization with a high rate in initial period and nucleation period was is inversely proportional to the surfactant concentration. The morphology of particles was sphere with core-shell structure. Mechanical testing results shows latex film composed with PUS IGM2000 is better than the one with PUS IGM1000.

scholarly journals Intra-axonal transport and turnover of neurophysins in the rat. A proposal for a possible origin of the minor neurophysin component

1973 ◽  
Vol 136 (4) ◽  
pp. 1047-1052 ◽  
Author(s):  
Graham D. Burford ◽  
Brian T. Pickering
Keyword(s):  
Axonal Transport ◽  
Rate Constant ◽  
Half Life ◽  
Minor Component ◽  
The Other ◽  
Metabolic Product ◽  
Exponential Rate ◽  
Neural Lobe ◽  
Intracisternal Injection ◽  
Kinetics Of

1. Radioactivity associated with the three neurophysins in the neural lobe of the rat was determined at intervals up to 5 weeks after an intracisternal injection of [35S]cysteine. 2. The radioactivity associated with the two major neurophysins (one supposedly associated with vasopressin and the other with oxytocin) increased linearly for 12h after the injection and the ratio of the rates of increase in the two proteins was very similar to the ratio of vasopressin to oxytocin in the gland. 3. From 12h onwards the radioactivity associated with each major neurophysin declined exponentially but the half-life of the supposed oxytocin–neurophysin (13.3 days) was shorter than that for the supposed vasopressin–neurophysin (19.8 days). 4. The kinetics of labelling of the minor neurophysin was quite different from that of the two major ones. It became slowly labelled during 3–5 days after injection and the radioactivity hardly decreased during the following 4 weeks. 5. The data could support the hypothesis that the minor neurophysin is a metabolic product of oxytocin–neurophysin. The exponential rate of disappearance of radioactivity from oxytocin–neurophysin and the minor component taken together has a rate constant similar to that for vasopressin–neurophysin (e.g. half-life=18.9 days).

The Mechanism Which Restricts Chain Growth in Polymerization with Alkylaluminum-Titanium Tetrachloride Complex Catalysts

1961 ◽  
Vol 34 (3) ◽  
pp. 986-990
Author(s):  
S. E. Bresler ◽  
M. I. Mosevitskiĭ ◽  
I. Ya Poddubnyĭ ◽  
Shi Guan-I
Keyword(s):  
Molecular Weight ◽  
Regular Structure ◽  
Chain Growth ◽  
Time Interval ◽  
Stationary Condition ◽  
Kinetics Of Polymerization ◽  
Molecular Weight Distributions ◽  
Weight Distributions ◽  
Kinetics Of ◽  
Isoprene Polymerization

Abstract In the production of polymers having a highly regular structure of the molecular chains, catalyst complexes of the Ziegler type are currently in wide use. The development of mechanisms for the separate steps in the catalytic process is of primary significance. This report outlines some results on a study of the mechanisms involved in isoprene polymerization with complexes formed through the interaction of Al (iso-C4H9)3 and TiCl4; the data were obtained from the sedimentation of the polymers in the ultracentrifuge, in combination with data on the kinetics of polymerization. We have indicated previously1 that in isoprene polymerization using the specified catalysts, the growth of the macromolecules proceeds quite rapidly, the time interval between the first appearance of active chains and the termination of reaction being only a few minutes; subsequently there follows an immediate stationary condition. However, with use of the ultracentrifuge we have obtained molecular weight distributions of polymers which are substantially different from the equilibrium distribution expected from present-day kinetic theories of polymerization. They were characterized by relatively low dispersion and, in the main, strongly distorted by high-molecular bands; in most cases, there was practically a complete absence of molecules with a molecular weight less than 200–300 thousand.

Detection of Low Molecular Size Lipopolysaccharide Contaminated in Dialysates used for Hemodialysis Therapy with Polyacrylamide Gel Electrophoresis in the Presence of Sodium Deoxycholate

1993 ◽  
Vol 16 (5) ◽  
pp. 245-248 ◽  
Author(s):  
T. Komuro ◽  
R. Nakazawa
Keyword(s):  
Gel Electrophoresis ◽  
Polyacrylamide Gel Electrophoresis ◽  
Aqueous Media ◽  
Molecular Size ◽  
Sodium Deoxycholate ◽  
Polyacrylamide Gel ◽  
The Other ◽  
Bacterial Endotoxin ◽  
Molecular Sizes ◽  
Dialysis Membranes

Dialysis membranes are generally considered to be impermeable for bacterial endotoxin (lipopolysaccharide, LPS) contaminated in dialysates used for hemodialysis therapy, since LPS molecular size in aqueous media has been reported to be more than 106. However, there are few reports concerning its size in dialysates. We have already presented a newly developed polyacrylamide gel electrophoresis with sodium deoxycholate (DOC-PAGE) which proves the LPS size. Using this method, therefore, we attempted to clarify the size of LPS in dialysates. We demonstrated that LPS in dialysates had roughly two different molecular sizes with DOC-PAGE and that compared to migration profiles of Salmonella LPS as controls on DOC-PAGE, one molecular size of LPS was approximately 4,000 and the other in tens of thousands. This investigation indicates the possibility of LPS transfer across dialysis membranes.

The polymerization of styrene by sulphuric acid - II. The kinetics of polymerization in 1:2-dichloroethane

1961 ◽  
Vol 263 (1312) ◽  
pp. 63-74 ◽  
Keyword(s):  
Rate Constants ◽  
Homogeneous Solution ◽  
The Other ◽  
Chain Reaction ◽  
Individual Values ◽  
Kinetics Of Polymerization ◽  
Temperature Range ◽  
Molecular Weights ◽  
Reaction Theory ◽  
Kinetics Of

The polymerization has been studied in homogeneous solution over the temperature range 0 to 35°C. At the upper temperatures the reactions are very fast; over the whole temperature range they are incomplete, giving limited yields of polymer which depend on the initial acid concentration, but not on that of the monomer. The results are described by the non­-stationary chain reaction theory derived in part I. Individual values of all the rate con­stants are obtained at 25°C, and ratios of rate constants at the other temperatures. The molecular weights are relatively low (< 20000) and determined by transfer rather than true termination processes.

Kinetics of Reactions of 8-Quinolinol and Acetate with Hydroxyaluminum Species in Aqueous Solutions. 2. Initial Solid Phases

1971 ◽  
Vol 49 (10) ◽  
pp. 1688-1690 ◽  
Author(s):  
R. C. Turner
Keyword(s):  
Aqueous Solutions ◽  
Solid Phase ◽  
The Other ◽  
Rate Determining Step ◽  
Rate Of Dissolution ◽  
Effects Of Ph ◽  
Solid Phases ◽  
The One ◽  
Kinetics Of ◽  
As If

The effects of pH and concentrations of 8-quinolinol and acetate on the rate of release of mononuclear Al from an initial solid phase formed by the rapid precipitation of mononuclear Al cations and from another formed by the precipitation of polynuclear hydroxyaluminum cations with NaOH were determined. With the solid formed by precipitation of the mononuclear Al cations, the rate was governed by the rate of dissolution of the solid. Dissolution occurred because the solution was undersaturated with respect to the solid. With the solid formed by the precipitation of the polynuclear cations the reaction behaved as if the rate determining step in the release of the mononuclear Al was the decomposition of the polynuclear cations after dissolution of the solid, indicating that the polynuclear cations persisted as such in the precipitate.Independent evidence that the two initial solid phases were entirely different was indicated by the fact that the one formed by precipitation of mononuclear cations developed into gibbsite in a few days whereas the other did not.

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