Effects of Pendant Ligand Binding Affinity on Chain Transfer for 1-Hexene Polymerization Catalyzed by Single-Site Zirconium Amine Bis-Phenolate Complexes

Abstract

The kinetics of 1-hexene polymerization using a family of five zirconium amine bis-phenolate catalysts, Zr[tBu-ON(X)O]Bn2 (where X = THF (1), pyridine (2), NMe2 (3), furan (4), and SMe (5)), has been investigated to uncover the mechanistic effect of varying the pendant ligand X. A model-based approach using a diverse set of data including monomer consumption, evolution of molecular weight, and end-group analysis was employed to determine each of the reaction specific rate constants involved in a given polymerization process. The mechanism of polymerization for 1-5 was similar and the necessary elementary reaction steps included initiation, normal propagation, misinsertion, recovery from misinsertion, and chain transfer. The latter reaction, chain transfer, featured monomer independent β-H elimination in 1-3 and monomer dependent β-H transfer in 4 and 5. Of all the rate constants, those for chain transfer showed the most variation, spanning 2 orders of magnitude (ca. (0.1-10) × 10(-3) s(-1) for vinylidene and (0.5-87) × 10(-4) s(-1) for vinylene). A quantitative structure-activity relationship was uncovered between the logarithm of the chain transfer rate constants and the Zr-X bond distance for catalysts 1-3. However, this trend is broken once the Zr-X bond distance elongates further, as is the case for catalysts 4 and 5, which operate primarily through a different mechanistic pathway. These findings underscore the importance of comprehensive kinetic modeling using a diverse set of multiresponse data, enabling the determination of robust kinetic constants and reaction mechanisms of catalytic olefin polymerization as part of the development of structure-activity relationships.

Quantification of active sites in single-site group 4 metal olefin polymerization catalysis

“…Thus, Bochmann and coworkers studied the polymerization of 1-hexene with the rac-{Me2Si(2-Me-Benz[e]Ind)2}ZrCl2/MAO system [40]. Consumption of the monomer was monitored by 1 H NMR with respect to an internal standard [46,35,[49][50][51][52][53][54][55][56][57] via analysis of aliquots sampled from the reaction mixture [40].…”

“…Using comparable conditions, the authors probed the influence of several parameters (nature of the metal center [52,55], ligand [53], temperature [57], etc). From this comprehensive work, several conclusions can be drawn concerning the fractions of active sites generated.…”

Copolymerization of 4-methyl-1-pentene with α,ω-alkenols

“…Studies on the polymerization of higher α-olefin have drawn considerable attention for long years. Polymerization of either linear or branched α-olefin has been fully explored by using various catalyst systems, including the traditional Ziegler-Natta catalyst [19,20], metallocene catalyst [21][22][23][24], non-metallocene single-site catalyst [25] and later transition metal catalyst [26,27]. Properties of poly(α-olefin) could be improved by incorporating the second monomer with a functional group, but the successful examples were limited so far [28,29].…”

Synthesis, characterization and catalytic properties for olefin polymerization of two new dimeric zirconium(IV) complexes having diamine-bis(phenolate) and chloride ligands

“…The presence of an extra donor on the pendant arm in these complexes leads to the catalysts which are extremely reactive in 1-olefin polymerization, while tridentate complexes with the same [ONO] ligand cores are rapidly deactivated and they give only traces of oligomers [3]. All complexes of that type investigated in the olefin polymerization reactions were monomeric and mostly apart from the dianionic diamine bis(phenolate) ligand they contained two benzyl groups as labile monoanionic groups [1][2][3][4][5]8,9,[11][12][13][14][15]. The reports on the synthesis of chloro-derivatives and their use in olefin (co)polymerization are very rare up to now [10,15].…”