Neodymium Components and Respective Catalyst Systems

In scientific and patent literature on diene polymerization the following Nd(III)-salts are most often cited as catalyst precursors halides, carboxylates, alcoholates, phosphates, phosphonates, allyl compounds, cyclopentadienyl derivatives, amides, boranes and acetylacetonates. The catalyst systems based on these Nd-sources are reviewed in the following subsections. 

The most important progress with NdX3-based systems is the addition of appropriate ligands or electron donors (D). Work in this area has been continued since 1980, when the first experiments were performed in China [92,109,110]. A first review of this work was published by Shen in 1987 [111]. 

The solubility of NdX3 catalysts is improved by the addition of electron donors (D). Catalyst activity is remarkably increased without substantial deterioration of the cis- 1,4-content. Typical donor ligands applied in NdX3 Dn/AlR3 type systems are alcohols such as EtOH [92,112,113], 2-ethylhexanol [114] or various pentanol isomers [115]. Furthermore, tetrahydrofuran (THF) [35], tributyl phosphate (TBP) [116-119], alkyl sulfoxides [116,117,120,121], propion amide [122,123], B(0-CH2-CH2-0-CH2-CH2-0H)3/B(0-CH2-CH2-0-C2H5)3 [124,125], pyridine [126] and dioxides [127,128] are applied as donors. The increase in catalyst activity by donor ligands is attributed to the improved solubility of the active species in hydrocarbon solvents [129,130]. 

A recent effort to increase the activity of NdCl3-based system comprises the use of NdCb nanoparticles. Kwag et al. succeeded in the preparation of nanosized NdCU 1.5 THF (particle size 92 nm). The nanosized NdCl3 was prepared in THF medium by dissolution of anhydrous NdC. Nanosized NdCl3 particles were obtained in a colloidal formation step during which THF is slowly replaced by cyclohexane upon addition [ 132], Catalyst activity is inversely proportional to the size of the NdCU nanoparticles. The activation of NdCl3 nanoparticles with DIBAH/TIBA results in catalyst activities which match the activities of standard Nd-carboxylate-based ternary sys- 

Neodymium halide n Donor Cocatalyst cis-1,4-Content/% Refs. 

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