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statistical model. The polymer structure is long sequences of racemic diads with only isolated meso-diads. The syndiotactic configuration results from the phenyl-phenyl repulsive interaction. (Figure 2). This is a result of the increased repulsive interactions between benzyl-type growing chain and the bulkier Cp (cyclo-pentadiene). Successive monomers approach from opposite sides of catalyst, but they are always pointing their phenyl group up. As a result, the phenyl group end up alternating sides of polymer chain. Figure 2. Steric control of syndiotactic polypropyleneExperimental Procedure: Materials. The following reagent were used as received: Toluene (99.9%), The metallocene catalyst precursor, cyclopentadienyl titanium trichloride CpTiCl3 (95%, Strem Chemicals), Tetrahydrofuran (THF, 99.9%, Fisher), MAO (98%, Akzo Chemical). Styrene. Table 1. List of materials for styrene polymerization Monomer Catalyst1 Ligand Solvent Temperature Description Styrene CpTiCl3 MAO Toluene 50 Ratio 500 1 75 Molecular Weight 104.15 219.36 58 Density(g/ml) 0.909 0.875 Moles 1.746E-02 3.491E-05 2.618E-03 Mass(g) 1.8180 0.0077 1.5186 Volume(ml) 2.00 1.7356 5.0
Polymerization.A clean dried schlenk tube is charged with a magnetic stirbar, CpTiCl3, Styrene, and Toluene. The tube is then degassed with at least three freeze, pump, thaw cycles under Ar and finally frozen in a dry ice/acetone bath. Methylaluminoxane (MAO) was prepared in-situ using wet start of tri-methyl aluminum. The reaction is place at 50C for approximately 23 hours. The final sample was precipitated as many times as necessary to produce a white powdered sample for NMR. Characterization.1H-NMR (500MHz) spectra were recorded on a Bruker DRX-500 at 25 C in CDCl3. GPC analyses were performed at 34 C on a Waters 150-C plus gel permeation chromatograph equipped with a Waters 410 differential refractometer, a Waters 2487 dual wavelength absorbance UV-Vis detector set at 254 nm. Tetrahydrofuran (THF) (Fisher; 99.9%) was used as eluent at a flow rate of ml/min. Number-average(Mn) and weight-average molecular weights (Mw) were determined from calibration plots with polystyrene standards.