Copolymerization of propylene and 1-hexene in the presence of homogeneous metallocene catalysts

The copolymerization of propylene and 1-hexene initiated by isospecific catalytic systems containin ansa-metallocene complexes with a C-2 symmetry, rac-Me2Si(Ind)(2)ZrCl2 and rac-Me2Si(4-Ph-2-Me-Ind)(2)ZrCl2), and a syndiospecific catalytic system based on a C-s symmetric complex Ph2C(Cp)(Flu)ZrCl2 was studied. Polymethylaluminoxane or a mixture of polymethylaluminoxane and Al-i-Bu-3 was used as a cocatalyst. The addition of small amounts of 1-hexene to the reaction mixture brings about activation of isospecific catalytic systems. The activity of 1-hexene in copolymerization varies in the sequence: rac-Me-2 Si(Ind)(2)ZrCl2 < rac-Me2Si(4-Ph-2-Me-Ind)(2)ZrCl2 < Ph2C(CP)(Flu)ZrCl2. It was shown that the resulting copolymers are characterized by a monomer unit distribution close to random (r(1)r(2) = 0.7-1.9). An optimum Al-i-Bu-3 : Zr ratio ensuring a marked reduction in the consumption of poly methylaluminoxane with a concomitant increase in the copolymer yield was determined. It was shown that the incorporation of even small amounts of 1-hexene (0.9-12.0 mol %) into PP chains leads to a decrease in its melting temperature and degree of crystallinity and causes an appreciable rise in the elasticity and impact strength of the final polymers.