Influence of stereospecificity and molecular weight on mechanical properties of iso-syndio-polypropylene obtained by combination of metallocene catalysts

Abstract Polypropylene with special properties can be obtained using two supported metallocene catalysts of different stereospecificities: rac-Me 2 Si(2-Me-benz[e]Ind) 2 ZrCl 2 [CAT-B] as an isotactic catalyst precursor and Ph 2 C(Cp)(9-Flu)ZrCl 2 [CAT-C] as a syndiospecific catalyst precursor supported on silica/MAO. These catalysts were evaluated either isolated or as a binary system. Catalysts physical mixtures and hybrid catalysts were prepared at three proportions, and tested in propylene polymerization. The effect to the activity and presence of hydrogen in the structural and mechanical properties of resultant polypropylenes were investigated. The influence of the binary systems containing more than half of the syndiotactic fraction on the molecular and mechanical properties respect to the isotactic polypropylene was evaluated. The great contribution of the sPP was observed in the polypropylene synthesized with the catalysts physical mixtures in absence of hydrogen. These samples showed a reduction of the crystallinity leading to an increase in the stress at break, because the flexion resistance is reduced. Polymers obtained with hybrid catalysts have an average molecular weight and crystallinity nearly to isotactic polypropylene with a break at very low strains, and high modulus.