Dissociated propagation species

Polymer Synthesis via Non-Dissociated Propagating Species Formed by... 

This chapter reviews reactions at high temperature via the non-dissociated propagating species carrying an oxo acid-derived counteranion. 

To visualize the synthetic versatility of the non-dissociated propagating species, two chapters are devoted to selective linear dimerization and living cationic polymerization, both using non-MX initiators and the nature of the non-MX -type counteranions has been discussed. Further comparison of MX and non-MX initiators is made in living cationic polymerization, and it has been proposed that the mechanisms to yield living polymers may differ, depending on the type of initiator. 

The most abundant propagating species must be the unpaired cation, i.e., the dissociation constant KD of the ion-pairs must be so great that the ratio y/p = [Pn+]/[Pn+A ] would be greater than 10, and preferably greater than 102. 

The results of Enikolopyan and co-workers [27, 28] on the polymerisation of styrene by perchloric acid at high pressures shed some new light on the problem. Essentially their kinetic results agree with those of Pepper and Reilly and of ourselves. The important feature of their findings is that the extent of acceleration by pressure is merely that which can be attributed to increase of dielectric constant of the solvent. There was no effect which could be attributed to increasing abundance of free ions by increased dissociation of ion-pairs. This means that, if the propagating species are ions, then they are all free ions even at normal pressure (which is reasonable), or the propagating species is non-ionic. 

Nucleophilic GTP proceeds by a dissociative mechanism in which the propagating centers are ionic—similar to other anionic polymerizations [Hertler, 1994, 1996 Quirk and Bidinger, 1989 Quirk et al., 1993 Webster, 1992, 2000]. The anionic propagating species XXVII is generated in low concentrations by nucleophilic displacement of the trimethylsilyl group by the nucleophilic catalyst (W+Nu ) ... 

Propagation of two-ended (bifunctional) propagating species often proceeds at a rate lower than that of the corresponding monoanion species as a result of triple-ion formation [Bhattacharyya et al., 1964 Smid, 2002]. For example, ionic dissociation of the counterion from one end of the cesium salt of a two-ended propagating species XXX yields XXXI in which the newly dissociated anionic center remains near the ion pair at the other end of... 

Aromatic amines are known as to be efficient inhibitors of hydrocarbon and polymer oxidation (see Chapters 15 and 19). Aliphatic amines are oxidized by dioxygen via the chain mechanism under mild conditions [1,2]. Peroxyl and hydroperoxyl radicals participate as chain propagating species in the chain oxidation of amines. The weakest C—H bonds in aliphatic amines are adjacent to the amine group. The bond dissociation energy (BDE) of C—H and N—H bonds of amines are collected in Table 9.1. One can see that the BDE of the N—H bond of the NH2 group is higher than the BDE of the a-C—H bond in the amine molecule. For example, DN = 418.4 kJ mol 1 and DC H = 400 kJmol-1 in methaneamine. However, the BDE of N—H bond of dialkylamine is lower than that of the C—H bond of... 

Apart from some experiments with methyl and /i-chloroethyl vinyl ethers the initiator concentrations employed were such that the initiating cations, and presumably the propagating species, were essentially dissociated from the corresponding counterion. Once again therefore this data is a measure of the reactivity of the free polymeric cations derived from the various monomers. Isobutyl vinyl ether is the monomer most widely studied, and as would be anticipated for free cationic reactivities, the data varies little with the counterion employed (SbClg or BF4), or indeed with the carbocation used as initiator (C7H7 or Ph3C+) under similar experimental conditions. 

Smith (29) showed that the polymerization of styrene by sodium ketyls with excess sodium produced low yields of isotactic polystyrene. Smith also believed that sodium ketyls initiated the styrene polymerization in the same way as the anionic alfin catalyst. Das, Feld and Szwarc (30) proposed that the lithium naphthalene polymerization of styrene occured through an anionic propagating species arising from the dissociation of the alkyllithium into ion pairs. These could arise from the dimeric styryllithium as a dialkyllithium anion and a lithium cation... 

Dissociation/Assodation Equilibria.—Further spectroscopic evidence has been forthcoming concerning the ion-pair equilibria of propagating species, in this instance poly(vinylbiphenyl) carboanions. As with caibocation systems the conductance technique also has been widely employed and continues to be so. ... 

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