Living carbocationic polymerization

Abstract

The living polymerization of isobutylene (IB) by thetrans-2,5-diacetoxy-2,5-dimethyl-3-hexene (DiOAcDMH ⁼₆ )/BCl₃ initiating system in 1,2-dichloroethane (DCE) in the −30 to +21°C range has been investigated. Well-definedtert-chlorine terminated polyisobutylenes ($^{\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle-}$}}{t} } Cl - PIB - Cl^{\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle-}$}}{t} }$) have been obtained at suitably low IB and DiOAcDMH ⁼₆ concentrations in the −30° to 0°C range. Theoretical$Cl^{\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle-}$}}{t} }$ end functionality ¯F_n ∼2.0 ±0.1 was demonstrated by dechlorination with sodium biphenyl coupled with titration using a chloride ion selective electrode, and by¹H NMR spectroscopy. The$^{\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle-}$}}{t} } Cl - PIB - Cl^{\underset{\raise0.3em\hbox{$\smash{\scriptscriptstyle-}$}}{t} }$ was quantitatively dehydrochlorinated to ∼CH₂C(CH₃) =CH₂ capped PIBs which in turn were quantitatively converted by hydroboration/peroxidation to ∼CH₂CH(CH₃)CH₂OH ended PIBs. The internal ∼C(CH₃)₂CH=CHC(CH₃)₂∼ initiator fragment in the polymer remains unchanged during end group functionalizations due to steric protection by thegem-dimethyl groups and the polymer chain.