Chromium catalysts for butadiene and norbornene polymerization

A new class of chromium catalysts were obtained by combining bidentate phosphine chromium(II) complexes with methylaluminoxanes. These systems were found to be very active in the polymerization of butadiene giving 1,2 polymers having different tacticity (iso or syndio) depending on the type of phosphine bonded to the chromium atom. Moreover, they were also able to polymerize norbornene, giving crystalline all exo-enchained vinyl addition polymers, exhibiting a rather unusual structure in the field of olefin stereospecific polymerization, namely diheterotactic structure, characterized by regular sequences of (mr) atactic triads.