The Low Pressure Fischer Polymerization of Ethylene with A1 + A1C1₃+ TiC1₄Revisited

Fischer in 1943 described the A1C1₃+ Al + TiCl₄catalyzed polymerization of ethylene to solid polyethylene at temperatures of 130–180 °C and pressures of 30–80 atm. No characterization of the polyethylene formed was given nor any mechanism suggested for the reaction. Recently, Martin et al. reinvestigated the Fischer polymerization and reported that the polyethylene obtained in admixture with Friedel-Crafts-type hydrocarbon oils is highly branched. In contrast, our reinvestigation of the Fischer polymerization of ethylene showed that if the temperature of the reaction mixture is kept in the range suggested by Fischer (130–180 °C) or below, besides Friedel-Crafts-type oils, linear high-density polyethylene similar to Ziegler polyethylene is obtained. Without proper temperature control, however, the exothermic reaction can lead to the results reported by Martin et al. Study of the mechanism of the Fischer polymerization indicates that the system is well suited for the in situ formation of ethylaluminum chlorides via the Hall and Nash reaction, as well as isomeric bis(dichloroaluminio)ethanes which, with TiCl₄, form the active Ziegler-Natta-type coordination polymerization catalysts.