SYNDIOSELECTIVE PROPYLENE POLYMERIZATION CATALYZED BY RAC-2,2-DIMETHYLPROPYLIDENE (1-ETA-5-CYCLOPENTADIENYL) (1-ETA-5-FLUORENYL)DICHLOROZIRCONIUM

Syndioselective propylene polymerization has been promoted by rac-2,2-dimethylpropylidene(1-eta5-cyclopentadienyl)-(1-eta5-fluorenyl)dichlorozirconium (1). The active catalytic species were generated using either triphenylcarbenium tetrakis (pentafluorophenyl) borate (2) (Zr+ method) or methylaluminoxane (MAO method). The former exhibited much higher activity than the latter, especially at low polymerization temperatures (T(p)). Syndiotactic poly(propylene) (s-PP) obtained at T(p) = -20-degrees-C has T(m) approaching 160-degrees-C, [rrrr] pentad fraction of 0.92 to 0.95, and 45% crystallinity (X(c)). It crystallized in two antichiral unit cells B and C. The C structure is favored by low temperature of polymerization, slow crystallization from melt, and annealing. The s-PP has M(w)BAR/M(n)BAR ranging from 3.6 to 4.4, which can be separated into stereoregular fractions soluble in heptane and hexane and stereoirregular fractions soluble in pentane, ether, and acetone. Therefore, this system cannot be considered to be a single-site catalyst. A parallel study was made on the isopropylidene (1-eta5-cyclopentadienyl)(1-eta5-fluorenyl)dichlorozirconium (3)/MAO catalyst. Molecular mechanics calculations were performed for all combinations of the configuration of asymmetric centers. The steric energy favors syndiotactic enchainment for both catalysts 1 and 3, with 1 forming the more syndioselective catalyst. (C) 1994 John Wiley & Sons, Inc.