Alkylation of lanthanidocene chloride complexes was performed with BuLi, Mg(Bu)(Oct), or an equimolar mixture of BuLi and AlH(iBu)2. In the case of the latter, chain transfer reactions were observed between neodymium and aluminium, and higher activities were obtained. The use of the silylene‐bridged complex, [Me2Si(3‐Me3SiC5H3)2]NdCl, in combination with BuLi and AlH(iBu)2 provided an efficient and unique catalyst for the copolymerization of ethylene with butadiene. Copolymers with high butadiene contents (up to 62 mol‐%) were synthesized. The microstructure of butadiene units was mostly trans‐1,4, and copolymers exhibited a strong alternating character. The influence of butadiene content on the thermal properties of the copolymers was also investigated.Copolymerization of ethylene with butadiene using 4/BuLi/AlH(iBu)2 (▪) and 2/BuLi/AlH(iBu)2 (▴).magnified imageCopolymerization of ethylene with butadiene using 4/BuLi/AlH(iBu)2 (▪) and 2/BuLi/AlH(iBu)2 (▴).
Thermal treatments under vacuum of conventional supported Ziegler-Natta precatalysts (MgCl 2 /TiCl 4 /Dibutylphthalate) were conducted to gradually remove titanium to modify the active sites distribution. Only limited detitanations of precatalysts were achieved paying attention not to chemically alter the internal donor (T < 150 8C). Used in combination with the required cocatalyst and external donor in the propylene slurry polymerization, the modified precatalysts exhibited a drop of activity versus decreasing titanium content but the distributed polymer properties are almost not affected (a slight narrowing of molecular weight distribution was observed). After a titanium chloride secondary impregnation (possibly done in presence of an additional Lewis base), activity resumed but polymer properties are once again unchanged. These findings highlight the difficulty to separate the different families of active sites and lead us to propose a cluster organization of titanium active sites. Active sites are composed of titanium clusters having a size distribution at the precatalyst surface, possessing a critical operating size and operating collectively in polymerization.
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