Zirconocene-catalyzed stereoselective cyclocopolymerization of 2-methyl-1,5-hexadiene with propylene

Abstract

The copolymerization of 2-methyl-1,5-hexadiene (MHD) with propylene has been studied with different single-site group 4 metal catalysts. Systems based on ansa-zirconocene precursors such as rac-{Me₂Si(2-Me-4-Ph-Ind}ZrCl₂ (1) and C₁- or C_S-symmetric ansa-{CpCR₂Flu}ZrCl₂ (2 and 3, respectively), once activated by MAO, are highly active (20–600 kg_pol g_cat⁻¹ h⁻¹ at 60–70 °C) and yield copolymers in which MHD is cyclopolymerized as methylene-(1-methyl)-1,3-cyclopentane (MMCP) units. ¹³C NMR studies revealed, depending on the symmetry of the precatalyst used, either highly isotactic (1, 2) or syndiotactic (3) polypropylene (PP) backbones, with isolated MMCP units. Fully trans-diastereoselective cyclopolymerization of MHD was observed with 1/MAO, while a mixture of trans and cis MMCP rings was observed with 2 and 3/MAO. The amount of MMCP units in PP (0.2–1.6 mol%) can be controlled by the amount of MHD in the feed. In contrast, the constrained geometry catalyst system based on {C₅Me₄SiMe₂NtBu}TiCl₂ (4) and MAO showed a much lower productivity (ca. 3 kg_pol g_cat⁻¹ h⁻¹ at 60 °C) and yielded a regioirregular, atactic copolymer in which MHD is simply vinyl-inserted in quite moderate amounts (0.2 mol%).