Constant, e values

The data indicate that the lowest power factor (100 x tan 6) and dielectric constant (e ) values, as measured at 150 C, are shown by the samples containing MTOP-DMP and MTBP-DMP. There would appear to be a trend in these electrical data in that the samples containing halide anionic species (e.g., chloride and iodide) apparently exhibit higher power factor and dielectric constant values than the non-halide phosphonium additives. This is not too surprising because of the more polar nature of the halide ions compared to anions such as dimethylphosphate. 

It should be noted that if the density-of-state curves calculated for the (periodic) constituent systems have the same shape but are shifted by a constant energy value, one can approximate i7(k, ) by a constant E valued and then, by comparing equations (4.50) and (4.64), one can use the equation... 

Those PASs that ranged from 35 to 53 wt% in PDMS content clearly show the upper and lower two transitions corresponding to hard aramid segments and soft PDMS segments, respectively. Between the two transitions there are rubbery plateaus that have somewhat constant E values. The thermomechanical spectrum showed that the nature and extent of rubbery plateaus were affected by varying the amount of PDMS. It can be seen that as the soft-segment content is increased, the value of the modulus corresponding to the rubbery plateau decreased and the PAS with 75 wt% of PDMS showed a very sharp drop in modulus. This drop in modulus at... 

The polarity of IL is one of the spedfic properties that distinguishes it from molecular solvents. The variation of the polarity of IL before and after its covalent immobilization on different polymers was semiquantitatively investigated by means of steady-state fluorescence spectroscopy using pyrene as a probe. Scheme 2.15 [69]. It suggested that the static dielectric constant (e) values deduced from the fluorescence experiments revealed an increase in the polarity of the polymers from e < 5 to e > 10-20 after immobilization of IL. Hence, an IL supported covalently on a polymer exhibits similar polarity as that of the bulk room-temperature IL. For example, the e of the IL [EMIm][NTf2 is 15.76. 

Solvent Effects on the Rate of Substitution by the S l Mechanism Table 8 6 lists the relative rate of solvolysis of tert butyl chloride m several media m order of increasing dielectric constant (e) Dielectric constant is a measure of the ability of a material m this case the solvent to moderate the force of attraction between oppositely charged par tides compared with that of a standard The standard dielectric is a vacuum which is assigned a value e of exactly 1 The higher the dielectric constant e the better the medium is able to support separated positively and negatively charged species 8olvents... 

For a growing radical chain that has monomer 1 at its radical end, its rate constant for combination with monomer 1 is designated and with monomer 2, Similady, for a chain with monomer 2 at its growing end, the rate constant for combination with monomer 2 is / 22 with monomer 1, The reactivity ratios may be calculated from Price-Alfrey and e values, which are given in Table 8 for the more important acryUc esters (87). The sequence distributions of numerous acryUc copolymers have been determined experimentally utilizing nmr techniques (88,89). Several review articles discuss copolymerization (84,85). 

Such data can provide a calibration curve and allow the constants (E) and F ) in equation (20) to be determined. The value of the molecular weight of an unknown solute can then be obtained from its (H) value by reading the value directly from the curve or by calculation using the predetermined constants (E) and (F ) in equation (20). It should be pointed out that an error of up to 30% may not appear to be very useful but, in fact, such precision can be extremely valuable in the preliminary examination of many biochemical substances where only very small quantities of material are available. It is also an ideal method for molecular weight determination before more accurate, labor-intensive and time-consuming methods are considered. 

Note. All values are with reference to the molarity scale. Data for bases are expressed as acidic ionisation constants e.g. for ammonia we quote pK at =9 245 for the ammonium ion... 

Substituent effects as evaluated on the basis of the Hammett equation and its extended forms, are - this has to be emphasized again — empirical results. Nevertheless, it is very soothing to know that theoretical approaches, i. e., calculations of substituent effects using ab initio molecular orbital theory (Topsom, 1976, 1981, 1983 Taft and Topsom, 1987, STO-3G and 4-31G level), give results that are consistent with the experimental data. However, it is not recommended to use only theoretically calculated substituent constants and values for F, R, and other parameters for the interpretation of experimental data. 

The a—time curves for the oxidation reactions [60] of both nickel maleate (534—568 K) and nickel fumarate (548—583 K) were similar to those characteristic of each reactant in vacuum, though E values were reduced to 150 10 kJ mole-1. It was concluded that the distributions of nucleation sites and subsequent patterns of product development were little altered by the change in composition of product from Ni/C (and Ni3C) to NiO. This difference, however, significantly changed the temperature coefficient and stoichiometry of the interface processes, since all carbonaceous material in the reactants was converted to CO2. A constant value of E (150 kJ mole-1) was thus found for the oxidations of the four nickel salts studied [60], the maleate, fumarate, formate and malonate. 

Waters61 have measured relative rates of p-toluenesulfonyl radical addition to substituted styrenes, deducing from the value of p + = — 0.50 in the Hammett plot that the sulfonyl radical has an electrophilic character (equation 21). Further indications that sulfonyl radicals are strongly electrophilic have been obtained by Takahara and coworkers62, who measured relative reactivities for the addition reactions of benzenesulfonyl radicals to various vinyl monomers and plotted rate constants versus Hammett s Alfrey-Price s e values these relative rates are spread over a wide range, for example, acrylonitrile (0.006), methyl methacrylate (0.08), styrene (1.00) and a-methylstyrene (3.21). The relative rates for the addition reaction of p-methylstyrene to styrene towards methane- and p-substituted benzenesulfonyl radicals are almost the same in accord with their type structure discussed earlier in this chapter. 

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