Efficient Synthesis of Aluminium- Terminated Polyethylene by Means of Irreversible Coordinative Chain- Transfer Polymerisation Using a Guanidinatotitanium Catalyst

A series of guanidinato-ligand-stabilised titanium complexes has been synthesised and characterised. These compounds can be prepared by carbodiimide insertion into titanium-amide bonds. Reaction of carbodiimides N,N-bis(2,6-diisopropylphenyl)carbodiimide, N,N-bis(2,6-dimethylphenyl)carbodiimide and N-tert-butyl-N-(2,6-diisopropylphenyl)carbodiimide (2a-2c, respectively) with [(Et2N)TiCl3] led to mono(guanidinato)trichloridotitanium(IV) complexes (3a-3c). Subsequent conversion with methylmagnesium chloride gave the corresponding trimethyl complexes (4a and 4b). Single-crystal X-ray diffraction analyses were carried out for all complexes. Compound 4a showed very high activities in the polymerisation of ethylene in the presence of very high amounts of triethylaluminium and undergoes polymeryl chain transfer to aluminium. Irreversible coordinative chain-transfer polymerisation and a unique combination of catalyst economy and high activity were observed. In the presence of 1000 equivalents of aluminium, a chain elongation of 83.3% could be achieved with an activity of 9900 kg(PE)mol(cat)(-1)h(-1)bar(-1). The influence of the steric demand of the ligand on the polymerisation capability is significant and was investigated too.