Propene polymerization was conducted at 0 °C by [t-BuNSiMe2Flu]TiMe2 combined with B(C6F5)3, MAO, or the MAO which had been dried in a vacuum and washed with hexane before use. The effect of cocatalyst was investigated under atmospheric pressure of propene in a semibatch system where polymerization rate was followed by the amount of propene consumed. The B(C6F5)3 system was deactivated within 30 min, while the MAO system showed steady polymerization rate. On the other hand, the activity of the dried MAO system was so high that the kinetic profile could not be evaluated precisely. The MAO system gave the low molecular weight polymer, and the number of polymer chains was more than 10 times higher than the amount of titanium complex employed. In the dried MAO system, however, the produced polymer showed the highest molecular weight and narrowest molecular weight distributions of about 1.2. The batchwise polymerization with the dried MAO system indicated that propene polymerization proceeded quantitatively regardless of the monomer charged, and the number-average molecular weight of the polymer obtained increased linearly against the polymer yield with keeping the molecular weight distribution narrow and the number of polymer chains constant. The results of postpolymerization testified that living polymerization proceeded under these conditions. The 13 C NMR measurement indicated that syndiotactic-rich polypropenes were produced in a highly regiospecific manner by this catalyst system.
Group 4 [g 1 :g 3 -tert-butyl(dimethylfluorenylsilyl)amido]dimethyl complexes [t-BuNSiMe 2 Flu]MMe 2 (M = Ti, 1; Zr, 2; Hf, 3) were synthesized in a one-pot synthesis starting from the ligand, MeLi and MCl 4 (M = Ti, Zr, Hf), respectively. The structures of these complexes were determined by X-ray crystallography and the results obtained revealed that the fluorenyl ligand coordinates to center metal in a g 3 -manner irrespective of center metal employed. Propylene polymerization was conducted at 0 or 20°C in toluene by 1-3 combined with dried methylaluminoxane (MAO), which was prepared from the toluene solutions of MAO by removing free trialkylaluminiums, and HNMe 2 PhB(C 6 F 5 ) 4 in the presence of triisobutylaluminium. The 1-dried MAO system gave the polymer with syndiotactic triad (rr) of 63% at 0°C, whereas 2 and 3 did not give any polymer in the same conditions. The 2-dried MAO system gave the polymer with the highest syndiotacticity (rr = 97%) at 20°C, although the activity was low. The 3-dried MAO system did not give any polymer even at 20°C. When HNMe 2 PhB(C 6 F 5 ) 4 was used in place of dried MAO at 20°C, 1 gave almost atactic polymer, while 2 and 3 gave highly syndiotactic one (rr > 90%). These results indicate that the catalytic performance strongly depended on the center metal of the ansafluorenylamidodimethyl complexes as well as cocatalysts employed.
Summary: Batchwise polymerization of propylene was conducted at 0 °C in heptane using [tert‐BuNSiMe2Flu]TiMe2 (1) combined with dried methylaluminoxane (MAO) and dried modified methylaluminoxane (MMAO), which were prepared from the toluene solutions of MAO and MMAO by removing the solvent and the free trialkylaluminium. The dried MMAO system quantitatively gave the polymer with higher molecular weight and narrower molecular weight distribution (MWD), ca. 1.3, compared with the dried MAO system. In addition, the polymerization with dried MMAO in toluene, chlorobenzene (CB) and ortho‐dichlorobenzene (o‐DCB), as solvent, also produced polymers quantitatively with MWD of ca. 1.1–1.3. The number‐average molecular weight ($\overline M _{\rm n}$) of the polymers, obtained with these systems, increased linearly against the polymer yield, while the narrow MWD was retained and the number of polymer chains was almost constant. The results of post‐polymerization in heptane and o‐DCB proved that the living polymerization proceeded irrespective of the solvent used. The semi‐batch polymerizations under an atmospheric pressure of propylene indicated that the propagation rate was more than 10 times higher in o‐DCB than in heptane. The 13C NMR analysis of the polymers indicated that the syndiotacticity also depended on the polarity of the solvent and increased in the following order: CB ≤ o‐DCB < toluene < heptane.A plausible scheme for the interaction between active species and solvents.imageA plausible scheme for the interaction between active species and solvents.
The atomic structure of the In on Si (111)(4×1) surface has been determined using direct methods applied to transmission electron diffraction data. It consists of a zigzag chain of In atoms and a region of silicon including a dimer chain. The structure is sufficiently similar to recent models of the Au on Si (111)(5×2) and metal on Si (111)(3×1) structures, that some preliminary generalizations on the linear n×1 and n×2 Si(111) reconstructions can be made.
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