Mechanism of initiation and propagation

Under substantially anhydrous conditions, the anionic polymerization of lactams possessing an unsubstituted amide group may be initiated by any strong base capable of forming the free lactam anion 

The acceleration at the start of the polymerization (Fig. 8, curve 1) represents an induction period in which certain active species are formed gradually. It has been established that the active chain growth centre is represented by an A/-acylated lactam [44, 83, 85—94] which is formed in the slow disproportionation reaction 

When an acyllactam is added at the beginning of polymerization, the induction period is absent (Fig. 8, curve 2). Hence, the anionic polymer- 

The polymer amide anion is in equilibrium with monomeric lactam and lactam anions are regenerated 

The net result of reactions (24) and (25) is the incorporation of one linear monomer unit into the polymer chain with regeneration of both the active end group and the lactam anion. 

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Refs 1) W.A. Taylor A. Weale, PrRoySoc 138A, 92-116(1932) (Mechanism of initiation and propagation of detonation in solid explosives) la) E. Burlot, CR 197, 1223-25 (1933) CA 28, 2538 (]934) (Ignition of explosives in vacuo) lb) A.F. Belyaev, DoklAkadN 18, 267 (1938) (Origination of detonation in explosives under the action of a thermal impulse) 2) A.F. Belyaev et al, KhimReferatZh 1940, No 10-11 CA 37, 1270(1943) (Investigation of initiation of small quantities of expls by heat with an impulse lasting for 10 3-10 secs, showed that the more volatile the expl, the harder... 

SocJ 30, 151-58(1960) (Recent advances in condensed media detonation) 37b) Dunkle s Syllabus (1960-1961), pp 4a 4b (Initiation of shock waves) lOa-lOg (Initiation of deflgrn and deton) p 12a (Frank-Kamenet-skii formulation) p 13b (Initiation by electric discharge) p 13f (Thermal Decomposition and Initiation of Explosives, as discussed by B. Reitzner) pp 17a to 17e (Mechanism of initiation and propagation of detonation in solid explosives) pp 17e 17f [Marlow Skidmore (Ref 31) concluded from their investigations that the problem of shock initiation is somehow related to the temperature distribution in the shock pulse and its effect on the chemical reaction rate. They used an Arrhenius type relationship for the rate increase in the frac-... 

Detonation (and Explosion), Mechanism of Initiation and Propagation of. See under Detonation (and Explosion), Initiation (Birth) and Propagation (Growth or Spread) in Explosive Substances... 

Kinetic Study and (he Possibility of Block Polymer Synthesis Mechanisms of Initiation and Propagation Reactions... 

The filament occurs on metals covered by an organic film and because of a certain discontinuity in the film, air and water penetrate through the coating and reach the underlying metal. This adjacent humid layer becomes saturated or rich in corrosive ions from soluble salts, and forms the zone called the active head of the filament. The dissolution of metal decreases as the solubility of the oxygen increases. The metallic ions oxidize and form compounds or corrosion products. These zones are called tails. Figure 6.22 illustrates a section and explains the mechanism of initiation and propagation of the filament. 

Step. However, the actual mechanism of initiation and propagation may not be simple... 

The duality in the mechanisms of initiation and propagation described above is reflected in the molecular weights and molecular distributions of the polymeric products. Thus, Stewart and Stahmann [43] found by column chromatography double-peaked distributions in poly-L-lysine samples prepared from e-benzyloxycarbonyl-L-lysine NCA by initiation with ammonia, the samples having both low and high molecular weight... 

There is no single mechanism for Ziegler-Natta polymerization because of the variety of catalyst and co-catalyst systems as well as the different phases in which the reaction may take place. The process of stereoregular polymerization can be understood tfom the mechanism of initiation and propagation as the monomer is inserted at the polymerization site on the catalyst surface. The detailed mechanism for achieving stereospecificity is an active area of research (Corradini and Busico, 1989, Tait and Watkins, 1989), but some general principles may be learned tfom the simple Ziegler-Natta catalysts (Allcock and Lampe, 1981). 

From these findings, and from results of the model reactions In Table I, which showed that the bulkier the substituent In the alcohol, the greater the participation of the 0-rlng opening, it Is possible to propose the following mechanism of Initiation and propagation for the polymerization of styrene oxide by the sodium methoxlde ... 

Describe metathesis polymerization of methyl cyclobutene, showing the mechanisms of initiation and propagation. 

Mechanisms of initiation and propagation of cracks Crack initiation... 

Detailed studies on the mechanisms of initiation and propagation of epoxide polymerization have been conducted using well-defined and stable initiators. Ethylene oxide (EO) was generally chosen as the reference monomer, owing to the living character of its polymerization, whereas the anionic polymerization of most other epoxides, including propylene oxide (POx), is subject to side reactions. 

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