Nature and concentration of active species in cationic polymerization of vinyl ethers: A kinetic investigation

Abstract

AbstractThe Kinetics of the polymerization of isopropyl vinyl ether, isobutyl vinyl ether (IBVE) and chloroethyl vinyl ether initiated by HI in CH2Cl2, in the presence and in the absence of tetrabutylammonium iodide as common anion salt, were investigated. The polymerizations proceed directly through the carbon–iodide termini without any necessary electrophilic activator. As previously observed with cyclohexyl vinyl ether, it was found that the addition of small amounts of salt, (0·5–10% with respect to initial [HI], depending on the monomer) drastically reduces the polymerization rate and leads to living‐type polymerizations. Higher amounts of salt have no influence on the polymerization rate which remains constant over a broad range of [NBu4I]/[HI] ratios. This general behaviour, observed for the all vinyl ethers, suggests a common ion salt effect and therefore an ionic polymerization mechanism involving ion pairs and free ions. In the absence of salt, both ion pairs and free ions of higher reactivity participate in the propagation, whereas only ion pairs contribute to the propagation in the presence of a common ion salt. According to this scheme, the living character of the polymerization is assumed to result from a propagation reaction governed by undissociated ionic species. The validity and the implications of this reaction scheme, in terms of active centre concentrations, are also discussed.