Living cationic polymerization of vinyl ethers and styrene derivatives: Design of initiating systems based on added salts with halogen anions

This paper overviews three living cationic polymerization systems (for styrene, p-methoxystyrene, and isobutyl vinyl ether) that are, in common, featured by: (i) specifically in nonpolar solvents, the use of the hydrogen halide/metal halide initiating systems (HX/MX_n; X: I, Br, Cl; MX_n: ZnX₂, SnCl₄), which generate a living growing carbocation stabilized by a nucleophilic counteranion (X^?…MX_n); (ii) specifically in polar solvents, the use of externally added ammonium salts (nBu₄N⁺Y^?; Y^?: I^?, Br^?, Cl^?), which permit the generation of living species from HX/MX_n by providing nucleophilic halogen anions Y^?, either the same as or different from the halogen X^? in HX.