Polymerization of ethene catalyzed by dicyclopentadienylzireonium dichloride/methylaluminoxane was performed in toluene at 50 degrees C under 0.38-8.95 bar ethene. Both Fourier-transform infrared spectroscopy and gel-permeation chromatography showed that the molecular weight is independent of the ethene pressure (concentration). The trans-vinylene unsaturation content increased as the pressure decreased. Termination by beta-H transfer to a coordinated monomer and a kinetically controlled isomerization reaction are suggested, in order to explain the observations.