Melt elasticity and catalyst structure

Catalysts on the basis of complexes of cobalt or iron salts [e.g., cobalt(II) chloride/ pyridine, cobalt(II) acetate/AlR2Cl] yield mixed structures with more than 20% 1,2 double bonds and rubber elastic-like polymers [325,326]. Rare earth catalysts have also been described [327]. A crystalline c/ -1,4 polymer with a melting point of 198°C and a molecular weight of 100 000 is obtained with aluminum alkyls/neodymium compounds at a molar ratio of 31 1. The yield is in the range of 30%. Cobalt(II) acetate in combination with diethylaluminum chloride or rhodium salts also yields a cis-, A polymer [328,329]. 

Figure 8 shows low shear rate rheological results for an ethylene homopolymer and an ethylene/1-hexene copolymer with catalyst 15/MAO [81]. Ethylene homopolymers by this catalyst exhibit the rheological behavior of linear chain polymers. In contrast, the copolymer displays a higher molecular weight and broader MWD than the corresponding ethylene homopolymers and, as shown in Fig. 8, in the copolymer melt the elastic behavior dominates even at the lowest frequencies. Behavior like this suggests the presence of widely different relaxation times, as in a crosslinked network structure (but the polymer was completely... 

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