Kinetics of propylene polymerization by hafnocene diamide catalyst

The kinetics of propylene polymerization initiated by ansa-metallocene diam ide compound rac-(EBI)Hf(NMe2)(2) (EBI = C2H4-(indenyl)(2), rac-1) were inv estigated. The rac-1 compound could be directly utilized for catalyst forma tions without converting to a dihalide or dialkyl complex in the presence o r absence of methylaluminoxane (MAO). The MAO-free system rac-1/AIR(3)/[Ph3 C][B(C6F5)(4)] (2) is much more effective than the rac-1/MAO catalyst. The activity of the rac-1/Al(iBu)(3)/2 system is much higher than that of the r ac-(EBI)HfCl2/MAO or rac-(EBI)ZrCl2/MAO catalyst, and almost same as that o f the rac-(EBI)Zr(NMe2)(2)/Al(iBu)(3)/2 catalyst under similar conditions. The alkylation of rac-1 to rac-(EBI)HfR2 by using AlR3 needs more time than the corresponding zirconocene analogue. The activity increases by a factor of 7 by increasing the aging time from 1 min to more than 4 h. The activit y of the rac-1/AlR3/2 catalyst is very sensitive to the type and concentrat ion of AlR3, and decreases in the order: Al(iBu)(2)H > Al(iBu)(3) > AlEt3 > AlMe3. The catalyst keeps high activity in a narrow range of the [Al]/[Hf] ratio. In addition, the activity is influenced by the concentration of 2, and as a result, the maximum activity is observed when 2/rac-1 = 0.7. The a ctivity of the rac-1/AlR3/2 catalyst is also sensitive to the polymerizatio n temperature. The activation energies for the initiation and overall react ions are calculated as 7.61 and 7.14 kcal/mol, respectively. The properties of polymer such as isotacticity (as [mmmm]), molecular weight (MW), molecu lar weight distribution (MWD), melting temperature (T-m), and crystallinity are similar level with those obtained with the rac-(EBI)HfCl2/MAO system. The MW and isotacticity of the polymer produced by MAO-free system decrease s monotonically as T-p increases, and MWD becomes narrow from 2.90 to 2.10 when T-p increases from 30 to 90 degrees C because of the compositional hom ogeneity of the polymer produced at high T-p, which is demonstrated by frac tionation of the polymer. Both MW and [mmmm] values of polymers decrease as aging time and anion concentration increase. (C) 2000 John Wiley & Sons, I nc.