Constant of initiator decomposition

Three different mechanisms of perester homolytic decay are known [3,4] splitting of the weakest O—O bond with the formation of alkoxyl and acyloxyl radicals, concerted fragmentation with simultaneous splitting of O—O and C—C(O) bonds [3,4], and some ortho-substituted benzoyl peresters are decomposed by the mechanism of decomposition with anchimeric assistance [3,4]. The rate constants of perester decomposition and values of e = k l2kd are collected in the Handbook of Radical Initiators [4]. The yield of cage reaction products increases with increasing viscosity of the solvent. 

The linear dependence between the activation energy of decomposition of the azocompounds RN2R and the BDE of the R—H bond (D(R—H)) was established [3], The rate constants of the decomposition of azo-compounds in the gas phase and hydrocarbon solvents have close values. The mean value of the rate constant of AIBN decomposition in hydrocarbon and aromatic solutions was recommended to bekd= 1015 x exp(— 127.5/RT) s-1 [2], The values of the activation energies and the rate constants of the decomposition of azo-compounds in the gas and liquid phases can be found in the Handbook of Radical Initiators [4],... 

The formation of radicals from hydrogen peroxide in cyclohexanol was measured by the free radical acceptor method [60] the effective rate constant of initiation was found to be equal to ki = 9.0 x 106 exp(—90.3/RT) s 1. For the first-order decomposition of H2O2 in an alcohol medium, the following reactions were discussed. 

Like the oxidation of hydrocarbons, the autocatalytic oxidation of polymers is induced by radicals produced by the decomposition of the hydroperoxyl groups. The rate constants of POOH decomposition can be determined from the induction period of polymer-inhibited oxidation, as well as from the kinetics of polymer autoxidation and oxygen uptake. The initial period of polymer oxidation obeys the parabolic equation [12]... 

Oxidation develops only if the rate of initiation is higher than the rate of generation of an efficient inhibitor. For the rate constants of sulfoxides decomposition, see Table 17.7. 

If hydroperoxide decomposition is rapid, then a quasistationary oxidation is established after the time t (A s[S]o) 1, and the quasistationary concentration [ROOH]st is given by the equation when the rate of chain initiation is very low [9] where kd is rate constant of ROOH decomposition. 

The values of the activation energies and the rate constants of the decomposition of azo-compounds in the gas and liquid phases can be found in the Handbook of Radical Initiators [4]. 

The thermochemical characteristics of l,3,5-trinitro-l,3,5-triazepane, such as energies of dissociation of N-NOz bonds, enthalpies of formation, vaporization, and combustion, as well as enthalpy of formation of amine radicals, have been determined <2004MI92>. The rate constants of initial monomolecular stages of thermal decomposition in the solid phase were measured for its furazano-fused analog 20 <1999RCB1250> and the ratio of the rate constants of decomposition in the melt and solid states, characterizing the reaction retardation in the crystal lattice, was determined. The kinetics of the thermal decomposition of 20 has also been studied <1995MI885>. 

The rate of radical generation or production (Rpr) is related to the rate constant for initiator decomposition, c, by Equation 10.3 where [I] is the instantaneous initiator concentration. The factor of 2 is included because two initiator or primary radicals are... 

A constant rate of absorption was observed (Figure 2). The efficiency of amine for terminating chain reactive oxidation is calculated according to the following reaction proposed by Hammond et al. (9), in which the rate constant of initiation kt was taken to be 8.16 X 10"4 mole/min. from the rate of evolution of nitrogen in a simple decomposition of azobisiso-butyronitrile in chlorobenzene at 62.5°C., and the efficiency e of initiator was taken to be 0.58 (10). 

Lakhinov et al. [56] observed an 8.5-fold increase in the rate constant of AIBN decomposition in methyl methacrylate caused by the presence of ZnCl/. The initiation rate increase more than fourfold (see Figs. 1 and 2), and the degree of polymerization falls more slowly with increasing concentration of initiator. The complexes of BF3 with AIBN decompose to radicals 14 times more rapidly than the azo initiator itself [59], thus making possible its use at around room temperature. 

A fourth and probably the most useful method of determination of initiator eflSciency is based on the dead-end effect in polymerization technique which is treated in a later section. This technique allows treatment of kinetic data obtained under dead-end conditions to evaluate both the rate constant for initiator decomposition (kj) and the initiator efficiency (/) under experimental conditions. 

In general the monomer concentration cm by far exceeds die initiator concentration ci and the rate constant of the termination reaction kr is much higher than the rate constant of the decomposition kn. This allows the formulation of the gross reaction rate with the help of the following approximation, which is still of satisfying accuracy ... 

In the above scheme M stands for the monomer concentration, I is the concentration of the initiator, and [R ] and [P ] mean the concentration of primary and polymer radicals, respectively S stands for the chain transferring agent, Ri denotes the decomposition rate of the initiator, and Rp the rate of polymerization. The rate constant for initiator decomposition is kd, for initiation is ki, for propagation Ap, and for termination is hr. The above is based on an assumption that kp and ki are independent of the sizes of the radicals. This is supported by experimental evidence, which shows that radical reactivity is not affected by the size, when the chain length exceeds dimer or trimer dimensions. ... 

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