Novel Nanostructures for Ethene-based Copolymers from a Penultimate Unit Effect

This work presents the enantioselectivity of a catalytic site as a key factor to control themicrostructure of ethene copolymers prepared through insertion copolymerization. Ethene/1-olefin copolymers were prepared with isospecific metallocenes and either propene or 4-methyl-1-pentene as the 1-olefin. Isospecific metallocenes were: (i) the moderately isospecific racethylenebis(indenyl)zirconium dichloride [rac-(EBI)ZrCl2] (EBI), (ii) the slightly more isospecific hydrogenated omologue, rac-ethylenebis(tetrahydroindenyl)zirconium dichloride [rac-(EBTHI)ZrCl2] (EBTHI), (iii) the highly regio- and iso-specific metallocene, rac-[methylenebis(3-tert-butyl-1-indenyl)]zirconium dichloride [rac-H2C-(3-tBuInd)2ZrCl2] (TBI), (iv) the most isospecific rac-[methylenebis(3-tert-butyl-cyclopentadienyl)]zirconium dichloride [rac-Me2C-(3-tBuCp)2ZrCl2] (TBC). The isospecific organometallic complexes TBI, EBI and EBTHI prepared copolymers with long sequences of both comonomers when 4-methyl-1-pentene was the 1-olefin, whereas, when propene was the 1-olefin, “blocky” copolymers were obtained only with the highly isospecific metallocenes TBI and TBC. A fine tuning of catalyst enantioselectivity is the key to prepare unusual copolymer microstructures, from almost “random” distribution of comonomers to long sequences of them. This paves the way for preparing, through an insertion chain copolymerization, ethene based elastomeric materials, from the amorphous ones to thermoplastic elastomers with a chance of selecting the comonomer the hard segment is made of.