High cis-1,4 polyisoprene or cis-1,4/3,4 binary polyisoprene synthesized using 2-(benzimidazolyl)-6-(1-(arylimino)ethyl)pyridine cobalt(II) dichlorides

Polyisoprene (PI) with a high content of cis-1,4 (up to 95%) or cis-1,4/3,4 binary structures was synthesized using a cobalt system in toluene. The cobalt system, which exhibited high activities (up to 3.50x10(6) g PI(mol Co)(-1)h(-1)), contained a series of 2-(benzimidazolyl)-6-(1-(arylimino)ethyl)pyridine cobalt(II) dichlorides activated with ethylaluminium sesquichloride. The nature of the ligands and the reaction conditions significantly affected both the catalytic performance of the cobalt complexes as well as the structures of the resultant PI. The stereospecific polymerization of isoprene could be tuned via changing either the co-catalyst or solvent: for example, increased content of 3,4 PI (up to 36.6%) was achievable in heptane in the presence of diethylaluminium chloride. Sequence distribution analysis by C-13 NMR spectroscopy indicated that most 3,4 units occurred randomly in the PI chains. (c) 2013 Society of Chemical Industry