Initiating systems with nucleophilic counteranion

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 first reported controlled/living polymerization of p-methylstyrene with acetyl perchlorate in the presence of HBU4NCIO4 [221] was based on the added salt method. Later, it was reported that cumyl acetate/ BC13 and related initiating systems induce controlled/living polymerizations of p-methylstyrene [117,222] and 1,3,5-trimethylstyrene [223]. The HI/ZnC(2 system, suited for vinyl ethers and p-alkoxystyrenes, can also be used for p-methylstyrene [224], but the lower reactivity of the monomer requires a much higher concentration of the zinc activator (ca. 100 mJW for 10 mM HI) to obtain a sufficient polymerization rate. These systems function without added nucleophilic additives and can be classified under the counteranion method. 

In controlled/living systems reactions B and C can be avoided or converted into reversible ones, if ligands such as fluorides are not used, if the concentration of moisture is very low in comparison with initiator and if weakly basic/nucleophilic components (additives, counteranions) are used. Contribution of reaction A is reduced at low temperatures but can not be eliminated completely. 

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