Polymerization of butadiene and isoprene with bis-immine, pyridyl-immine and keto-immine vanadium complexes based catalysts

Vanadium catalysts are mainly known in the field of stereospecific diene polymerization for their ability to give highly trans-1,4 polymers, and are by far the most important systems for preparing trans-1,4 polybutadiene1. The heterogeneous systems obtained by combining vanadium halides (e.g., VCl3, VCl4) with aluminum alkyls (e.g., AlEt3, AlEt2Cl) gave a crystalline, high molecular weight, trans-1,4 polybutadiene (trans-1,4 content, 99-100%) with a melting point of about 130°C. Highly trans-1,4 polybutadiene, but with lower molecular weight and melting point, could also be obtained with the soluble systems VCl3?3THF-AlEt2Cl, V(acac)3-AlEt2Cl (acac = acetylacetonate) and V(acac)3-MAO. Some other soluble vanadium catalysts however (e.g., V(acac)3-AlEt3) have some interest for the preparation of syndiotactic 1,2-polybutadiene, while the metallocene systems (i.e., Cp2VCl/MAO and CpVCl2(PEt3)3/MAO) were found to give predominantly cis-1,4 polybutadiene (cis content about 85%) with a quite good activity2. More recently predominantly trans-1,4 poly(butadiene)s were also obtained with catalysts based on bis(imino)pyridyl vanadium(III) complex; the activity was however very low3. We have now synthesized and characterized some novel vanadium complexes with bis-immine, pyridyl-immine and keto-immine ligands. All the above complexes have been used in combination with aluminoxanes for the polymerization of 1,3-butadiene and isoprene. Polymers having different structure, ranging from 1,4 to predominantly 1,2 (3,4 in case of isoprene) were obtained essentially depending on the type of ligand on the vanadium atom and on the polymerization conditions (i.e., type of aluminoxane, polymerization temperature and polymerization solvent). The most significant results obtained are reported in the present communication. 1 L. Porri, A. Giarrusso, In Comprehensive Polymer Science, G.C. Eastmond, A. Ledwith, S. Russo, P. Sigwalt Eds., Pergamon press Ltd., Oxford, 1989, Vol. 4, Part II, pp 53-108. 2 G. Ricci, A. Panagia, L. Porri Polymer 1996, 37, 363-365. 3 E. Colamarco, S. Milione, C. Cuomo, A. Grassi, Macromol. Rapid Commun. 2004, 25, 450-454.