Mechanism of propagation

An intriguing question may be posed is the lifetime of living polymers prolonged by keeping them supplied with their monomer The answer depends on the mechanism of propagation. In many systems propagation takes place directly in one step ... 

The order of reactivities could be also reversed by a change of solvent. For example, in THF styrene is more reactive than butadiene towards salts of polystyryl anions, whereas in hydrocarbon solvents butadiene is more reactive than styrene towards lithium polystyrene. This reversal of reactivities presumably is caused by a change in the mechanism of propagation. The monomers react directly with carbanions in THF, but become coordinated to Li+ in hydrocarbon solvents. 

In the quasi-detonation regime, the continuous periodic detonation failure owing to diffraction by the obstacles and reinitiation by shock reflections constitutes the principal mechanism of propagation. 

Experiments involving explosions of molten tin and water are described [1], and the mechanism of propagation of the thermal explosions was studied [2], The dynamics of explosive interaction between multiple drops of molten tin and water has been examined experimentally [3],... 

The polymerization of olefins and di-olefins is one of the most important targets in polymer science. This review article describes recent progress in this field and deals with organo-transition metal complexes as polymerization catalysts. Recent developments in organometallic chemistry have prompted us to find a precise description of the mechanism of propagation, chain transfer, and termination steps in the homogeneously metal-assisted polymerization of olefins and diolefins. Thus, this development provides an idea for designing any catalyst systems that are of interest in industry. 

Young RC, Zhang P 2001 The mechanism of propagation of intracellular calcium waves in cultured human uterine myocytes. Am J Obstet Gynecol 184 1228-1234... 

A)Ya.B. Zel dovich, "Teoriya Goreniya i Detonatsii v Gazakh (Theory of Combustion and Detonation in Gases), TipogrAkadNauk, Moscow (1944) B) G.N. Abramovich L.A. Vulis, DoklAkadN 55, 111 (1947) (On the mechanics of propagation of detonation and combustion) C) Ya.B. Zel dovich K.S. Zarembo, ZhFizKhimii 22, 427(1948) (Investigation of a structure of a Bunsen flame)... 

IV,A. Existence, Uniqueness, and Mechanism of Propagation of. Deflagration Waves. It is... 

On the mechanism of explosive reaction. An attempt to apply the theory of chain reactions to certain phenomena observed in expls) 12)K.K.Andreev Yu.Khariton, TransFarad Soc 31, No 168 (1935) (On the mechanism of propagation of reactions by chain) 13)C.N.Hurshelwood, ZAngewChem 49, 370... 

Secondly, to explain the different mechanisms of propagation and transfer and the evolution of the microstructures. The experimental conditions are summed up in Table 2. 

The high rate of NCA polymerisation initiated by aprotie bases is its most remarkable kinetic feature. This is due to the high rate of propagation since the concentration of growing species appears to be low. It is apparent, therefore, that the mechanism of propagation of this reaction differs from that postulated for the primary amine-initiated polymerisation. 

Two additional mechanisms of propagation should be considered. In the presence of strong bases such as sodium methoxide or sodium triphenyl methyl, the terminal amine may be converted, at least partially, into respective sodium amide. Hence, the following propagation may ensue under these conditions,... 

The basic problem is raised by the second question, namely, which mechanism of propagation operates in the polymerisation giving the high molecular weight polypeptide. The writer proposes, therefore, the following experiment which may resolve the present controversy. Let us prepare a radio-active salt of carbamic acid, say,... 

The decarboxylation of carbamie acid shifts the equilibrium to the right, and the "activated NCA would then initiate Bamford s type of propagation. This is essentially the test proposed in the earlier paragraph by the writer, and its result should unequivocally discriminate between the two rival mechanisms of propagation. 

The mechanism of propagation is very effective as a defense mechanism when it is oriented toward bacteria or virus membranes, but it may be very inappropriate once it is directed against the host membranes (lipoproteins, endothelial cells, internal membranes, etc.). 

Bowey, F. A., NMR Investigations on the Mechanism of Propagation in Vinyl Polymerisation , in High Resolution NMR of Macromolecules, Academic Press, New York, 1972, pp. 146-181. 

The ratio of linear and cyclic macromolecules will be sharply affected by a change in the kinetics and mechanism of propagation, e. g. by transition from growth on activated chain ends to polymerization with activated monomer. An inactive macromolecule cannot produce macrocycles, neither by back- nor by end-biting reactions [339],... 

Carbocationic propagation involves repetitive electrophilic addition of carbenium ions to alkenes. This section discusses the mechanism of propagation by carbenium ions and also potential participation of other species in the chain growth. 

Propagation is the most important elementary reaction in which a macro-molecular chain is formed. Control in new carbocationic polymerizations, in which well-defined polymers are prepared, might be explained by new mechanisms of propagation and new types of active centers involved. However, as discussed briefly in Section IV.B.4, we believe that only two types of species with different degrees of ionization are involved sp3-hybridized dormant species and sp2-hybridized carbenium ions [Eq. (43)] ... 

The very straightforward results concerning the mechanism of propagation and cyclization in the polymerization of cyclosiloxanes were obtained by studying the radiation-induced cationic polymerization of 6-, 8-, and 10-membered cyclic siloxanes (D3, D4, Ds) [252,253]. 

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