Catalyst Systems and their Components

Standard Nd-based catalysts comprise binary and ternary systems. Binary systems consist of Nd chloride and an aluminum alkyl or a magnesium alkyl compound. In ternary catalyst systems a halide free Nd-precursor such as a Nd-carboxylate is combined with an Al- or Mg-alkyl plus a halide donor. By the addition of halide donors to halide-free catalyst systems catalyst activities and cis- 1,4-contents are significantly increased. In quaternary catalyst systems a solubilizing agent for either the Nd-salt or for the halide donor is used in addition to the components used in ternary systems. There are even more complex catalyst systems which are described in the patent literature. These systems comprise up to eight different catalyst components. 

The various components of a catalyst system are either dosed separately to the monomer solution (in simultaneous or consecutive way) or are premixed prior to the addition to the monomer solution (often referred to as preformed and/or aged , see Sect. 2.1.6). Beside the chemical nature of the catalyst components their order of addition (Sect. 2.1.6) plays an important role regarding the heterogeneity of the catalyst system, the polymerization activity and the polydispersity of the resulting polymer. 

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