Monomers monomolecular reactions

This stage can also happen earlier if electroneutral impurities, e.g. water, are present in the system. In this case, termination on this admixture is a monomolecular reaction, and the exponent is equal to unity. This equation makes it possible to evaluate the propagation rate constant kp for the free-ion process of radiation-induced polymerization. The values of v and kt are determined, for example, by varying the electrical conductivity of the monomer in the radiation field. 

In contrast to small organic molecules, longmass diffusion, but also by small-scale diffusion of a few monomer units. It is generally observed that even monomolecular reactions could happen only if these motions are unfrozen. In the wider sense, the dependence of reaction efficiency on polymer morphological structures can be described in terms of the free volume concept, and of diffusion constants [6]. These molecular characteristics are themselves dependent on the thermal transitions in polymers, the most important of which being ffie glass transition temperature. 

The theoretical scheme took into account the reaction of chain propagation limitation by transfer to the Al-organic compound, monomer, and hydrogen, as well as the chain termination following the monomolecular mechanism (spontaneous termination or the immurement of active center). 

For ethylene polymerization with lithium catalysts the most probable chain transfer reactions include (1) monomolecular elimination of LiH, (2) bimolecular displacement of the polymer by monomer, (3) metalation of monomer, and (4) metalation of solvent as shown below. 

It should be borne in mind that each activated monomer and polymer should only react with nonactivated monomer (addition polymerization) in both of these chemical examples. Reaction between an activated monomer and another activated monomer or a polymer (polycondensation) should not occur. With cyclophane, the mathematical treatment of the consecutive equilibria yields different expressions to those given in Table 16-1, since the /7-cyclophane, as initial monomer unit, yields two activated monomer molecules, and each reaction with activated monomer and its successive products yields only species with uneven numbers of structural elements. In addition, the polymerization of p-cyclophane is no longer a living polymerization when the degrees of polymerization are low, since, in this case, monomolecular (that is, intramolecular) termination reactions leading to the formation of inactive rings can occur. 

Pseudophase models, as well as other forms of quantitatively analyzing the effects of supramolecular aggregates on reaction rates, were derived for micellar solutions [21]. The full description, as well as critical analysis of the models, has been reviewed [22]. Pseudophase models start by considering that a system can be treated as if it were composed of two separate pseudophases, micelles and an intermicellar aqueous phase. It is further assumed that monomers, substrates and ions equilibrate much faster than reaction rates. This last assumption renders these treatments only applicable to some ground state reactions, since excited state processes and some electron transfer reactions, can be faster than equilibration rates [21,23]. Further assuming that the reaction rate in the two pseudophases can be characterized by two separate and independent rate constants (k, in the micelle and in the intermicellar aqueous phase) the rate constant kij/) of a spontaneous monomolecular decomposition of a substrate S is described by... 

The effect of excimer kinetics on fluorescence decays of monomers and excimers upon excitation with a short pulse was studied first by Birks et al. [119]. They took into account all the relevant processes that proceed after the excitation of a low fraction of monomers by an ultrashort pulse and derived the rate equations describing the monomer and excimer decays. Most processes involved in the Birks scheme are monomolecular and depend only on the concentration of the excited species and on the first-order rate constant one of them is a bimolecular process and depends on the concentrations of both the excited and ground-state molecules. They include (1) monomer fluorescence, (rate constant fM), (2) internal monomer quenching, M —>M, ( iM). (3) excimer formation, M - -M D (bimolecular reaction, i.e., the rate depends on the product of the rate constant and concentration of the ground-state... 

In the system where the chain reaction can develop, initiation with the known specified rate is created by either the introduction of an initiator, which decomposes to radicals with the known rate constant, or photochemically, or under the action of penetrating radiation (y beams, P beams). The dependence of the chain reaction rate V on the initiation rate v, allows one to judge about the character of chain termination. If V v chain termination has the first order with respect to the concentration of active centers if v v/, it has the second order. In the liquid phase in the absence of an inhibitor, chains termination is monomolecular, and the rate of the chain reaction, e.g., polymerization of the monomer M, is... 

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