Search

A single zirconium-based constrained geometry catalyst (Me2Si(1-C29H36)(1-N-tBu)ZrCl2·OEt2/methylaluminoxane) has been employed to produce homopolymers of ethylene which contain degrees of branching unprecedented for early transition metal systems. A variable density of long branches is observed (10−50 branches per thousand carbon atoms) with strong dependences on both polymerization temperature and pressure. These branches are attributed to the exceptionally facile incorporation of long -olefin macromonomers formed in situvia the usual -hydride elimination of polymer chains. Additionally, a relatively constant low degree of ethyl branches is observed (∼5 branches per thousand carbon atoms) under all polymerization conditions; this is attributed to -hydride transfer to monomer followed by immediate reinsertion of the coordinated olefin-terminated polymer into the formed metal−ethyl bond. [ABSTRACT FROM AUTHOR]

X-ray diffraction analyses of dimethyl ansa-metallocenes (CH3)2C(C5H4)(C29H36)M(CH3)2(M Zr or Hf) have revealed diffuse diffraction bands in the 0kland h0lsingle-crystal reciprocal lattice images, but not in the hk0plane. This is consistent with metallic disorder in two dimensions and constitutes a rare example of diffuse diffraction for an organometallic compound. The metal is apparently partitioned between two sites with a 60:40 occupancy ratio. Structural interpretation of the X-ray data is consistent with a 60:40 ratio of parallel/antiparallel (z, −z) metallocene pillars dispersed in the x−ydirections. Diffuse diffractionalbeit weakeris also observed for the half-metallocene (C29H37)Mn(CO)3, which occupies parallel/antiparallel pillars in an 80:20 ratio. [ABSTRACT FROM AUTHOR]