Cationic polymerization of isobutylene by FeCl3/ether complexes in hexanes: An investigation of the steric and electronic effects of ethers

The polymerization of isobutylene (IB) in hexanes at 0 °C initiated by tert-butylchloride (t-BuCl) and coinitiated by GaCl3 or FeCl3•diisopropyl ether (i-Pr2O) complexes to produce polyisobutylene with high exo olefin content (HR PIB) has been previously reported [1]. In an effort to further improve the efficiency of the catalytic system, we have performed systematic studies on the effect of the nature of the ether used in the FeCl3•ether complex on the polymerization. Investigation of the properties of the FeCl3•ether complexes possessing unique steric and electronic properties via attenuated total reflectance (ATR) FT-IR, and solubility studies have revealed several interesting characteristics that may be useful in further optimizing the present initiating system. For example, long alkyl chains reduce the solubility of the catalyst resulting in decreased polymerization rates. On the other hand, the polymerization rate can be increased by incorporating electron-withdrawing groups on the ether, which affects both the complexation equilibrium and the basicity of the ether. These investigations have identified key characteristics that should be present in the ether in order to increase reactivity while maintaining high levels of exo-olefin in HR PIB.