In-Situ Direct Analysis of the Growing Species by 119Sn NMR Spectroscopy: Living Cationic Polymerization of Isobutyl Vinyl Ether with HCl/SnCl4/nBu4NCl1
119Sn NMR spectroscopy was employed for analysis of the interaction and reaction of SnCl4 with the HCl-IBVE adduct [1; CH3CHCl(OiBu)] in the presence of nBu4NCl in CH2Cl2 solution at -78 degreesC, which are model reactions for the living cationic polymerization of isobutyl vinyl ether (IBVE). The addition of 1 to an SnCl4 solution led to upfield shifts of the tin nucleus as the 1/SnCl4 mole ratio (<1) increases, which indicates the formation of SnCl5-, via the interaction between SnCl4 and the chlorine atom in 1. On further addition of 1, the pentacoordinated anion is converted into the hexacoordinated SnCl62-. These tin species are in fast equilibrium among each other, and the 119Sn NMR analyses support the formation of a carbocation [2; CH3CH+(OiBu)] from 1 and the dynamic equilibrium between 1 and 2. More effective chloride-anion donors such as nBu4NCl and Ph3CCl can quantitatively convert SnCl4 into SnCl5-, and then into SnCl62-. Thus under the conditions where living cationic IBVE polymerization proceeds (1 < nBu4NCl/SnCl4 < 2), SnCl4 is fully converted into a weaker Lewis acid, SnCl5-, with the aid of added nBu4NCl. The suppression of the carbocationic species in the living system has thus been found due to the interaction between the added salt and SnCl4.
Katayama
H
Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 606-8501, Japan.
Kamigaito
M
Sawamoto
M