Initiation direction dependence

In the above scheme, a ligand L is exchanged by L in A to give B. The relative donicities of A and B, that determine the type of initiation, directly depend on the 3T-acceptor properties of L and L the following order of the relative donicities is opposite to that of the Jt-acceptor properties ... 

The initiation of the lactam polymerization with water is directly dependent on the water concentration ... 

Case 1 appears to accurately predict the observed dependence on persulfate concentration. Furthermore, as [Q]+otal approaches [KX], the polymerization rate tends to become independent of quat salt concentration, thus qualitatively explaining the relative insensitivity to [Aliquat 336]. The major problem lies in explaining the observed dependency on [MMA]. There are a number of circumstances in free radical polymerizations under which the order in monomer concentration becomes >1 (18). This may occur, for example, if the rate of initiation is dependent upon monomer concentration. A particular case of this type occurs when the initiator efficiency varies directly with [M], leading to Rp a [M]. Such a situation may exist under our polymerization conditions. In earlier studies on the decomposition of aqueous solutions of potassium persulfate in the presence of 18-crown-6 we showed (19) that the crown entered into redox reactions with persulfate (Scheme 3). Crematy (16) has postulated similar reactions with quat salts. Competition between MMA and the quat salt thus could influence the initiation rate. In addition, increases in solution polarity with increasing [MMA] are expected to exert some, although perhaps minor, effect on Rp. Further studies are obviously necessary to fully understand these polymerization systems. 

It was soon discovered that there were other solar system objects that were older and had more primitive strontium than the basaltic achondrites. Table 8.3 compares the (87Sr/86Sr)o value determined for BABI with those from some other important samples from the early solar system. If Allende, Angra dos Reis, and the basaltic achondrites formed directly from the solar nebula, then the time intervals shown in the right-hand column of Table 8.3 are valid. Note that the uncertainties on these time intervals, a few million years, are much smaller than the uncertainty in the eucrite isochron shown in Figure 8.9 ( 260 Myr). However, the validity of the time intervals determined from the initial ratios depends completely on the validity of the idea that they all formed directly from the bulk material of the solar nebula. 

For each initiator there is a useful temperature range for which the initiator decomposition rate constant, kd, will produce radicals at suitable rates for polymerization. The initiation rate is usually controlled by the decomposition rate of the initiator, which depends directly on its concentration (first-order reaction). The temperature window can be enlarged by the use of catalysts such as a tertiary amine (Eq. (2.80)), or an organometallic compound in a redox reaction (Eqs (2.81) and (2.82)). 

In what follows we will discuss the mechanism that controls the electron transmission through OOTFs, the resonances expected in the energy resolved transmission and how the dependence of the transmission on the initial direction of the electrons affects the temperature dependence of the transmission. 

The first value corresponds to tangency in point B and is the critical temperature defined above, while the second one corresponds to tangency in the high temperature region (surroundings of point D) and is discarded. The value of % does not directly depend on the particular choice of the initial temperature but the existence of... 

It is generally quite pure however, since purity is directly dependent upon conversion which in turn depends upon flow rate and temperature, initial preparations could result in products contaminated with cyclopentadiene. If this should occur, the magnesium cyclopentadienide could be purified by sublimation in vacuo after the contaminant has dimerized. 

The treatment of experimental data is an essential activity to calculate precise kinetic variables in the equations above. The quality of the kinetic analysis, the identification of relevant phenomena and, subsequently, model parameter fitting, are directly dependent on the initial data. 

It is of interest both in theoretical and practical aspect to arrange a more direct dependence between the character of changes in initial energy characteristics of atom and value of chemical bond energy. 

The small discrepency in initiation rate dependency between radiation (0.4) and chemically initiated systems (0.5) is interpreted as an artifact of the radiation initiation process. We have interpreted this in terms of a loss of initiation efficiency due to a low concentration of monomer in the aqueous phase. A similar effect has been observed in a study by Acres and Dalton (19.) where the intensity exponent was shown to be directly related to monomer concentration. 

Figure 7. The inverse temperature dependence of initial viscosity and direct dependence of cure chemorheology for poly(urea-urethane) adhesives yield activation energies of 9-12 Kcal/mole for viscous flow and 6-8 Kcal/mole for overall cure, respectively.

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