Polymerization of 1,3-dienes with neodymium catalysts

Neodymium catalysts are typical for the cis polymerization of 1,3-dienes. The systems prepared from a neodymium-carboxylate, a chlorine donor and A1(i-C₄H₉)₃ are characterized by a low efficiency, only ca. 6% of the neodymium being active in the catalysis. Much more active systems are obtained using allyl derivatives of neodymium in combination with aluminoxanes, in particular with methylaluminoxane (MAO). These systems have the characteristics of a single site catalyst. Evidence suggesting an ionic structure for the catalytic species is reported. Terminally substituted butadienes give polymers with a cis-1,4 isotactic structure, with the exception of (E, E)-2,4-hexadiene, which gives trans-1,4 polymers. An interpretation is reported.