Partially hydrolyzed trimethylaluminum (PHT) as heterogeneous cocatalyst for the polymerization of olefins with metallocene complexes

Abstract

A method for the preparation of a novel heterogeneous cocatalyst, partially hydrolyzed trimethylaluminum (PHT), has been developed and optimized for ethylene polymerization reactions. It is possible to generate PHT on nearly any support without much loss of catalyst activity. The carrier material can be SiO2, AlF3, B2O3, starch, cellulose, active carbon, polyethylene, polypropylene, polystyrene, etc. This new type of partially hydrolyzed trimethylaluminum (PHT) is synthesized by reacting such a carrier material with trimethylaluminum (TMA) in toluene to block all surface Lewis basic centers that could poison a cationic metallocene polymerization center. The subsequent addition of a calculated amount of water gives a heterogeneous PHT that is different from the common methylalumoxane (MAO). Various PHT cocatalysts were studied by 13C and 27Al MAS NMR, scanning electron microscopy (SEM), and infrared spectroscopy (IR), and compared with solid MAO. Surface areas and porosities were determined according to the BET method. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 454–466, 2001

Transition Metal-Catalyzed and MAO-Assisted Olefin Polymerization; Cyclic Isomers of Sinn’s Dimer Are Excellent Ligands in Iron Complexes and Great Methylating Reagents

“…The Ω r values all are greater than 10 kcal/mol, and in strong support of our hypothesis. Both 7 and 5 gave Ω r values of ∆G ≈ 16 kcal/mol for the phenyl-substituted ligands with a small preference ∆Ω r (10,12). The respective Ω r values for the methyl-substituted ligands are smaller and vary more; ∆G ≈ 10 kcal/mol for 7 and ∆G ≈ 15 kcal/mol for 5, respectively.…”

“…The computed oxophilicities Ω r are summarized in Table 3 and we discuss the ∆G values. The difference values ∆Ω r (10,12) and ∆Ω r (19,21) allow for a comparison of the two cyclic species 7 and 5, and ∆Ω r < 0 indicates that 5 is more strongly bonded ligand. The Ω r values all are greater than 10 kcal/mol, and in strong support of our hypothesis.…”

“…Ziegler-Natta polymerization [1,2] is the dominant method for the production of polyolefin [3,4]. Ziegler-Natta catalysts usually contain transition metal complexes (i.e., TiCl 4 ) and partially hydrolyzed aluminum alkyls as co-catalyst, among which methylaluminoxane [5][6][7] (MAO) is most commonly used today [8][9][10]. It was a major advance in the field when Brookhart discovered that Fe(II) complexes with di-nitrogen or tri-nitrogen ligands can serve as pre-catalyst with satisfying catalytic activity [11][12][13].…”

Synthesis and Characterization of High-Molecular-Weight PLAs with a Well-Controlled Particle Morphology

“…Polylactide (PLA) is one of the most promising biopolymers, showing excellent renewability, biodegradability, and biocompatibility. , Unfortunately, the applications of PLA are somewhat restricted because of its very slow crystallization kinetics, negatively affecting its mechanical properties. Studies addressing the crystallization in quiescent and flow conditions to quantify the crystallization rate and explain the mechanism of crystallization are reported in the literature. − Much efforts have been made to enhance the crystallization kinetics of PLA, in particular focusing on the incorporation of nucleating agents − and particles − (different silica sizes). Addition of crystal-nucleating agents is a simple, convenient, and efficient method to improve the crystallization rate of polymers, such as polypropylene and PLA. , For example, an aryl amide derivative with high melting point and good solubility in the PLA melt and silicated clay has been reported to be an efficient nucleating agent for PLA crystallization thanks to the epitaxial growth of PLA on the filler.…”