Living cationic polymerization of isobutyl vinyl ether by hydrogen chloride/Lewis acid initiating systems in the presence of salts: in-situ direct NMR analysis of the growing species

Abstract

Cationic polymerization of isobutyl vinyl ether (IBVE) was carried out with use of the HC1-IBVE adduct [1: CH3CH(OiBu)Cl]/Lewis acid (MX") initiating systems in CH2CI2 at -15 °C. Living polymers were obtained with 1 in conjunction with weak Lewis acids such as ZnCl2 and SnBr4; in contrast, the 1/MX" initiating systems with strong Lewis acids (SnCl4, TiCl4, and EtAlCl2) gave nonliving polymers. However, on addition of ammonium salts (nBu4N+Y~) and phosphonium salts (nBu4P+Y) carrying nucleophilic anions (Y~= Cl", Br, I", CH3CO2"), well-defined living polymers were indeed obtained (Mw/Mn ~1.1) with the SnCl4-based system. As model reactions of these living and nonliving polymerizations, a series of mixtures of 1 and MX" in the presence and absence of the salts were analyzed in CH2CI2 at -78 °C or above directly by NMR spectroscopy. Upon mixing SnCl4 with 1, the -methine and the pendant methylene absorptions of 1 shifted remarkably downfield (e.g., up to ca. 10 ppm for the former), and the extent of the downfield shifts increased with increasing SnCl4 concentration. On further addition of the salts with nucleophilic anions, the downfield signals returned to the original upfield position for the covalent adduct 1 alone. Thus, l/SnCl4 generates an ionic growing species that is in a rapid equilibrium with the covalent precursor 1, and the salts suppress the ionic dissociation of the growing carbocation to induce living cationic polymerization.

Major Progress in Catalysts for Living Cationic Polymerization of Isobutyl Vinyl Ether: Effectiveness of a Variety of Conventional Metal Halides

“…; Chart 2A]. 1,18,23,25 Another method is the use of additives, weak Lewis bases or ammonium salts. Most of the Lewis acids belong to this category.…”

Near-monodisperse,n-alkyl, end-functionalized poly(methyl vinyl ether)s: Synthesis by living cationic polymerization and solution characterization

“…9 In 1990, the hydrogen iodide/zinc iodide initiating system in the same solvent and at the same temperature as the previous system was employed for the synthesis of MVE homopolymers and block copolymers with p-methoxy styrene. 21 Finally, in 1993, the IBVE-HCl/nBu 4 NCl/SnCl 4 in dichloromethane at Ϫ78°C was used to polymerize MVE to give homopolymers 22 as well as block copolymers with styrene. 18 This last system was used as the initiator in our synthesis.…”

New stage in living cationic polymerization: An array of effective Lewis acid catalysts and fast living polymerization in seconds

“…[19][20][21] The results from these investigations suggested that the stabilization of the propagating carbocation through the nucleophilic interaction was of key importance. Along with the development of initiating systems, Higashimura's group, including Sawamoto and us, achieved the living cationic polymerization of various types of functional monomers to give end-functionalized, block, and star-shaped polymers.…”