Isospecific Living Polymerization of 1-Hexene by a Readily Available Nonmetallocene C₂-Symmetrical Zirconium Catalyst

Salalen Titanium Complexes in the Highly Isospecific Polymerization of 1‐Hexene and Propylene

“…[13] The ability of the dibenzyl complexes to promote isospecific polymerization in the presence of cocatalysts such as B(C 6 F 5 ) 3 or methylalumoxane (MAO) depends on the steric bulk of the phenolate substituents and on the metal.…”

“…However, the very high polymer molecular weights (M n = 360 000-390 000) relative to the calculated values (M calcd = 9300-48 000; obtained by dividing the amount of polymer obtained by mole of precatalyst employed) indicate partial precatalyst activation under these conditions. 13 C NMR spectroscopy revealed that the degree of isotacticity in these polymers depended on the size of the halide substituent, with [mmmm] = 63 % (Cl), 79 % (Br), and 94 % (I). Replacing the tBu substituent in Lig 3 with either a larger substituent (Ad, Lig 4 ) or a much smaller substituent (H, Lig 5 ) had little effect on the isotacticity of the resulting poly(1-hexene) ([mmmm] = 89 % and 87 %, respectively).…”

“…For example, Lig 6 H 2 , a salalen ligand precursor featuring the bulky adamantylphenolate on the imine side arm and a dibromophenolate on the amine side arm, led to [Lig 6 TiBn 2 ] as a single diastereomer (Scheme 2). Polymerization of liquid propylene yielded crystalline polypropylene with an extremely high degree of stereoregularity ([mmmm] = 99.6 %) and an even higher degree of regioregularity (no observable peaks between d = 30 and 45 ppm), as apparent from its 13 C NMR spectrum (Figure 3). Correspondingly, it exhibited a very high T m of 168.3 8C.…”

Exploiting Threefold Symmetry in Asymmetric Catalysis: The Case of Tris(oxazolinyl)ethanes (“Trisox”)

“…[33] The activity of 36 200 kg mol À1 h À1 (Table 2) is comparable to the extremely high activities reported for zirconium-amine-bis(phenoxide) complexes. [35] Upon reducing the polymerisation temperature to À30 8C, the activity dropped to 2030 kg mol À1 h À1 ; however, at this temperature Figure 5). [36] Although the iPr-trisox ligand readily adapts to a wide range of ionic radii, we were unable to successfully prepare complexes with the lanthanides preceding dysprosium, possibly owing to the decreased stability of lanthanide alkyl complexes as the ionic radius increases.…”

FI Catalyst for Polymerization of Olefin

“…Living polymerization is known to control some elements like as degree of polymerization, chainend structures, stereochemistry, especially molecular weight and chain-end structures of polymer. Although there have been a number of transition metal catalysts which can polymerize ethylene or -olefins in a living fashion [66][67][68] there are few catalysts that are useful for both ethylene and -olefins. Besides, most catalysts require a low polymerization temperature, usually below room temperature, to suppress chain termination and therefore exhibit low activities and insufficient polymer molecular weights.…”