Initiating systems with nucleophilic

Initiating Systems with Nucleophilic Counteranions The first generation of initiating systems for vinyl ether controlled/living polymerizations consists of a protonic acid (HB, initiator) with a Lewis acid (MtX , activator), [63,69,70]. The reported examples ofHB and MtX ... 

J. Initiating Systems with Nucleophilic Counteranions For isobutene, this group refers almost exclusively to the BCh-based initiating systems without external additives. As listed in Table 3.A, combinations of BCl3 with tertiary esters, ethers (methoxides), or alcohols induce controlled/living polymerization of isobutene in CH3C1 or other solvents at temperatures below -30° C. Scheme 10 illustrates the proposed pathway for the polymerization initiated with the cumyl acetate (12)/BC13 system [35] ... 

The major approach to extending the lifetime of propagating species involves reversible conversion of the active centers to dormant species such as covalent esters or halides by using initiation systems with Lewis acids that supply an appropriate nucleophilic counterion. The equilibrium betweem dormant covalent species and active ion pairs and free ions is driven further toward the dormant species by the common ion effect—by adding a salt that supplies the same counterion as supplied by the Lewis acid. Free ions are absent in most systems most of the species present are dormant covalent species with much smaller amounts of active ion pairs. Further, the components of the reaction system are chosen so that there is a dynamic fast equilibrium between active and dormant species, as the rates of deactivation and activation are faster than the propagation and transfer rates. The overall result is a slower but more controlled reaction with the important features of living polymerization (Sec. 3-15). 

The sequential living polymerizations for these syntheses begun with isobutene, initiated by the ferf-alkyl chloride or methoxide/TiCU initiating systems with a nucleophilic additive such as dimethylacetoamide (DMA)... 

The most characteristic reactions for these compounds are thermolysis and decomposition under the action of both acids and nucleophilic reagents. 1,2,4-Dioxazolidines 15 are thermally stable only below 100 °C. The thermolysis of compound 15a in solution at 130 °C afforded benzophenone and benzamide in quantitative yields. The formation of these products is consistent with a radical mechanism involving initial 0-0 homolysis (Scheme 21). The base-catalyzed decomposition of compound 15a afforded the same products. Similar results were observed for the decomposition of compounds 15b and 15c. The interaction of dioxazolidine 15a with triphenylphosphine resulted in deoxygenation of the system with the concomitant formation of benzophenone and its imine with aniline <1995J(P1)41>. 

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