Gegen ion

Anionic Polymerization. Addition polymerization may also be initiated and propagated by anions (23—26), eg, in the polymerization of styrene with -butyUithium. The LL gegen ion, held electrostatically in... 

Addition of metallic oxides to isobutene polymerized by high energy radiation leads to a spectacular increase in the yield.313. It seems that some ions are stabilized by complexing with the surface of the oxide and such an interaction prevents their recombination with the gegen-ions. These observations confirm therefore the suggested cause of inefficient ionic polymerization in systems exposed to ionizing radiation. 

The nature of the gegen ion is probably of the greatest importance in determining the rate of propagation in ionic polymerization. However, it is not clear whether the presence of the gegen ion enhances or inhibits the propagation. One may argue that the... 

Ions and ion pairs interact strongly with the solvent, and hence an ionic polymerization is greatly influenced by the environment. Solvation tends to separate the ions and thus the system approaches a state which would be expected in a hypothetical solution deprived of gegen ions. At the same time formation of a solvation shell around the growing center probably slows down the addition. This effect is particularly notable in the termination step and will be discussed further in the next section of this paper. 

In an ionic polymerization the strong electrostatic field of the ion pairs should have a pronounced effect on the ratio of the probabilities of the two placements. Furthermore, solvation of an ion pair is much stronger than of a neutral radical, hence the influence of a solvent on stereospecificity of addition is expected to be much more pronounced in an ionic polymerization than in a radical polymerization. The nature of the gegen ion represents still another factor which is of extreme importance in determining the stereospecificity of the polymerization. 

The tetrahedral configuration is further stabilized if the gegen ion is close to the carbanion. 

There are gegen ions, e.g. (BF3OH) ion, which cannot form a bond with a carbonium ion. Protogenic acids yielding such gegen ions are on the whole better initiators of carbonium ion polymeri-... 

One might anticipate that this type of termination in carbonium ion polymerization might be minimized or even completely avoided by complexing the gegen ion with a suitable electron-seeking molecule. Experiments designed with this purpose in mind are presently underway in our laboratories. If the termination could be prevented we would be able to synthesize living carbonium ion polymers. 

Gaussian elimination technique, 291 Gaussian wave function, 276 Gegen ions, 160... 

The gegen ion, K+, has been dismissed from the scheme in consideration of the comparatively high dielectric constant of the liquid ammonia medium.) The associated kinetic equations are equivalent to Eqs. (44) and (45). It will be observed that the termination step (51) is essentially a chain transfer with solvent. A similar process has... 

If F l, corresponding to a small external electrolyte concentration Cs compared with the concentration ic jz- of gegen ions belonging to the polymer, and if we further restrict ourselves to the case of a binary electrolyte for which z = z- = z and consequently v+ — v = l and v = 2j then the appropriate series expansion of Eq. (B-6) is... 

Here (26) is an intimate ion pair in which the jointly solvated gegen-ions are in very close association with no solvent molecules between them, (27) is a solvent-separated ion pair, and (28) represents the now dissociated, and separately solvated, pair of ions. 

In a solvolysis reaction, attack on R by a solvent molecule, e.g. H20 , in (26) is likely to lead to inversion, as attack can take place (by the solvent envelope) on the back side of R , but not on the front side where there are no solvent molecules, and which is shielded by the Bre gegen ion. Attack in (27) is more likely to lead to attack from either side, leading to racemisation, while attack on (28) can clearly happen with equal facility from either side. Thus the longer the life of R , i.e. the longer it escapes nucleophilic attack, the greater the proportion of racemisation that we should expect to occur. The life of R is likely to be longer the more stable it is—(a) above—but the shorter the more powerfully nucleophilic the solvent—(b) above. 

It is evident from Table XV that the gegen ion in (XXII) has a marked effect on the specificity of the catalyst. There is a marked change from... 

The flocculation concentrations of mono-, di-, and trivalent gegen ions should, from this theory, be expected as... 

Rose Bengal differs in reactivity from fluorescein and Eosin because of the iodines at C-2, C-4, C-5, and C-7 which differentiate the reactivity of the phenoxide from the carboxylate and make substitution at C-2 possible in lieu of substitution at C-6. Essentially three different kinds of Rose Bengal derivatives have been synthesized. The most common include derivatives with gegen ions other than sodium at both C-2 and C-6. Many esters of C-2 have been synthesized and compounds with a number of different gegen ions at C-6 have been reported. The rarest derivatives of Rose Bengal are the C-6 ethers, of which only three have been reported. 

Bawn and Ledwith [3) have extended the work on the solvolysis of threo-3-anisyl-2-butyl by Winstein and Robinson (5). Bawn and Ledwith showed that polymerization catalysts can be considered as having a complete range of ionic character from covalent to ionic. This spectrum can be extended both to cationic initiating species and to anionic initiating species with a complete range of degrees of freedom between the ionic species and their gegen ions. Fig. 1 shows this spectrum. In all of the subsequent discussion in this paper the shorthand notation... 

The experimental information shows that isotactic polymethylmethacrylate also requires the proper balance of ionic association between the propagating ion and its gegen ion. Dialkylmagnesium alone is too... 

These results are summarized in Fig. 5. With the anionic polymerization of styrene a balance of interaction between the propagating anion and the gegen ion is required. The ionic requirements for this balance... 

It is therefore apparent that the catalysts which produce isotactic polypropylene have an ionicity which, rather than anionic, is cationic, as shown in Fig. 8. The propagation in polypropylene involves the secondary cation which is closely associated and balanced with its catalyst gegen ion. This balance is dependent on the electron releasing effect of the methyl group at the propagating end of the double bond. 

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