Homogeneous binary zirconocenium catalyst systems for propylene polymerization .1. Isotactic/atactic interfacial compatibilized polymers having thermoplastic elastomeric properties

Polypropylene with thermoplastic elastomeric properties was synthesized by homopolymerization of propylene using two metallocene catalysts of different stereospecificities: rac-ethylenebis(1-eta(5)-indenyl)zirconium dichloride or rac-dimethylsilylenebis(1-eta(5)-indenyl)zirconium dichloride as isospecific catalyst precursors and ethylenebis(9-eta(5)-fluorenyl)zirconium dichloride as an aspecific precursor. The catalysts formed by activation of the precursors with triphenylcarbenium tetrakis( pentafluorophenyl)borate and triisobutylaluminum exhibit a very high activity of 5 x 10(7) g of PP/([Zr][C3H6] h). Products ranging from tough plastomers to weak elastomers were obtained by varying the ratio of the two types of precursors. The polymers containing less than half of the isotactic fraction display excellent thermoplastic elastomeric properties, which is attributable to an interconnected crystalline superstructure in an amorphous continuum compatibilized and bound together by a stereoblock copolymer at the interface against macrophase separation. Materials exhibiting elastic recoveries of 97-98%, which are relatively independent of elongation up to 500%, were obtained.