Concentration live different types

The study of the stereoregularity of the polymers prepared, provides also Information about the stereoregulating mechanism. The probability of formation of the different types of sequences, was determined on the basis of the resonance of the quaternary carbon of pVP (12). The NMR spectrum performed at 15 MHz allows one to determine the concentration of triads. The values summarized In Table 4 do not agree with those expected for bernoullllan statistics. Hence, more than the last unit of the living chain Is Involved In the process. In order to obtain more precise Information about the process, It is necessary to measure the probability of formation of pentads. Such measurements are possible with spectra performed at 63 MHz (Figure 18). In spite... 

As has already been mentioned, picosecond pulsed radiolysis offers great possibilities for studying the short-lived transient processes. In Ref. 326 the solutions of 2,5-diphenyloxazol (DPO) in different solvents were irradiated by picosecond electron pulses obtained from an accelerator. The authors have found two types of excitations of DPO, which they have named the fast and the slow excitations. With fast excitation the luminescence appears during the electron pulse and stops growing at the end of the pulse, after 10 ps. With slow excitation the luminescence is formed within 1 ns. At small DPO concentrations the observed intensity of fast luminescence cannot be explained by direct excitation by electrons (cf. data of Ref. 325). Analyzing the results of experiments with different solvents and different types of additives, Katsumura et al.326 conclude that the main part of the fast luminescence of DPO is due to VCR absorption. 

The major exposure of the population to natural radiation arises from inhalation of the short-lived radioactive progeny of the radioactive noble gas radon-222, which in turn is a sixth-generation radioactive decay product of natural uranium. The amount of radon-222 present in the air depends on many factors (e.g., gas permeability in soil and rock, relative humidity, and barometric pressure) but is necessarily linked to the geological concentration of the uranium parent radionuclide. There is about an eightfold range of concentrations of uranium in different types of rocks and soils. 

The reactions controlling the lifetime of ozone at the surface depend on the chemical composition of the aqueous film. If this is not specified, it is therefore not possible to estimate the steady-state concentration for this photooxidant in the aqueous phase. However, the chemical effect of ozone in films or atmospheric droplets can be estimated by assuming that the steady-state concentration of ozone is still in equilibrium with the concentration of the ozone in the atmosphere. An atmospheric concentration of ozone of 1012 molecules per cubic centimeter would result in an aqueous equilibrium concentration of about 1 nanomolar (20°C) as the environmental factor to be considered in the aqueous film. Figure 7 gives examples for the rate constants for different types of compounds and a scale for the corresponding half-lives of these compounds exposed to the estimated concentration of ozone. (For further rate constants see Ncta et al., 1988 or Hoigne and Bader, 1983 and Hoigne et al., 1985). 

Examples of the different types of living cationic polymerization systems are listed in Table 3. All involve relatively fast initiation and optimal equilibria between a low concentration of active carbenium ions and a high concentration of dormant species (Scheme 9). Only hydroiodic acid initiated polymerizations of A-vinyl carbazol are controlled in the absence of a Lewis acid activator or a nulceophilic deactivator [115]. 

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