A process for producing halogen-free, reactive polyisobutene

The invention relates to a method for producing reactive halogen-free polyisobutene containing more than 60 mole % terminal double bonds and having a mean molecular weight Mn of between 800 and 3,000 dalton, by cationic polymerization of isobutene in the liquid phase on an acid, substantially halogen-free heterogeneous catalyst. According to said method a) an isobutene-containing hydrocarbon mixture which consists essentially of C4 hydrocarbons and contains between 10 and 80 % by weight isobutene is used as educt; and b) continuous polymerization is carried out at between -30 and 0 DEG C and mean dwell times of the educt of no more than one hour, the temperature and dwell time being chosen such that isobutene conversion is less than 60 %. After separation of the resulting polyisobutene present in the fully reacted hydrocarbon mixture the isobutene is either enriched and returned to the polymerization stage or fed to another isobutene conversion stage which is coupled to the polymerization stage.