DETERMINATION OF THE NUMBER OF ACTIVE-CENTERS AND OF THE PROPAGATION RATE-CONSTANT FOR ETHYLENE POLYMERIZATION ON SUPPORTED NI-CONTAINING CATALYSTS BY USING (CO)-C-14

Ethylene polymerization on supported Ni-containing catalysts was studi ed using (CO)-C-14 as the inhibitor and as a label for determining the number of active centers (AC). The polymerization rate decreases shar ply after introducing a mole ratio (CO)-C-14/Ni = 0.5 divided by 1 and recovers after the removal of (CO)-C-14. The number of labels in the polymer and in the liquid phase (hexane) increases with the amount of (CO)-C-14 introduced and with (CO)-C-14 contact time (tau(co)). In the absence of ethylene the number of labels in the polymer does not incr ease with tau(co) and the number of labels in the liquid phase is esse ntially less than in the presence of ethylene. The rate of the label a ccumulation in the polymer during short contact times (tau(co) less th an or equal to 5 min) is essentially higher than that during the follo wing periods of time (tau(co) = 5-135 min). Fast label accumulation oc curs through first (CO)-C-14 molecule insertion into the Ni-polymer bo nd, and the slower one through copolymerization of (CO)-C-14 with ethy lene, i.e. when the second and more (CO)-C-14 molecules insert into th e polymer chain. Catalyst activity and the number of AC tin the range of 1.5 to 6% of Ni content) decrease with polymerization time. For bot h catalysts the values of the propagation rate constant are maximum at short polymerization time (5 to 15 min) and equal to (3 +/- 0.8).10(3 ) L/(mol.s) at 65 degrees C.