LLDPE with exclusively ethyl branches by tandem catalysis with single-site Zr(IV)/Co(II) catalysts

Semicrystalline linear low density polyethylenes
(LLDPEs) with exclusively ethyl branching (from 7 to 56
branches per 1,000 carbon atoms) were prepared from ethylene
by homogeneous tandem catalytic systems comprising
(imino)pyridine cobalt(II) dichlorides as oligomerization
precursors, bis(cyclopentadienyl)zirconium(IV) dichloride
as copolymerization precursor and methyaluminoxane as
activator. The activity of the tandem systems was evaluated
by varying either the molar fraction of the cobalt precursors
or the ethylene pressure. The latter parameter was of crucial
importance to control both the productivity and the extent of
1-butene incorporation. In particular, increasing the ethylene
pressure from 2 bar to 4 bar changed the ''comonomer
effect'' from positive to negative.