Gennadii D. Bukatov

Propylene Ziegler-Natta Polymerization: Numbers and Propagation Rate Constants for Stereospecific and Non-Stereospecific Centers

The data on the number of active centers (C p ) and values of propagation rate constants (K p ) have been obtained for stereospecific and non-stereospecific centers at propylene polymerization with catalytic systems of various composition: TiCl 3 -AlEt 3 (I), TiCl 4 /D/MgCl 2 -AlEt 3 (II), TiCl 4 /D/MgCl 2 -AlEt 3 -TES (III), where D - dibutyl phthalate, TES - tetraethoxysilane. The C p and K p values were determined by 14 CO quenching method at the polymerization in the basence and the presence of hydrogen. The C p and K p values were determined for three PP fractions: bioling pentane soluble fraction (atactic PP), boiling heptane soluble fraction (stereoblock PP) and boiling heptane soluble fraction (isotactic PP). The following result are obtained. (i) The K p values increased in the following order: atactic centers < stereoblock centers < isotactic centers (from ≃200 to ≃3.10 3 l/mol.s, 70°C) for all catalysts studies. (ii) The respective K p values od not differ essentially with the change of the catalyst composition (systems I, II, III). (iii) As the external donor is introduced in TMC (system III), the portion of stereospecific active centers increases (from 34 to 62%), but the total number of active centers changes insignificantly. MOst likely the non-stereospecific active centers transform into stereospecific ones in the presence of silane.

Determination of the number of active centers and of the propagation rate constant for ethylene polymerization on supported Ni-containing catalysts by using 14CO

Ethylene polymerization on supported Ni-containing catalysts was studied using 14 CO as the inhibitor and as a label for determining the number of active centers (AC). The polymerization rate decreases sharply after introducing a mole ratio 14 CO/Ni = 0.5/1 and recovers after the removal of 14 CO. The number of labels in the polymer and in the liquid phase (hexane) increases with the amount of 14 CO introduced and with 14 CO contact time (τ co ). In the absence of ethylene the number of labels in the polymer does not increase with τ co and the number of labels in the liquid phase is essentially less than in the presence of ethylene. The rate of the label accumulation in the polymer during short contact times (τ co ≤ 5 min) is essentially higher than that during the following periods of time (τ co = 5-135 min). Fast label accumulation occurs through first 14 CO molecule insertion into the Ni-polymer bond, and the slower one through copolymerization of 14 CO with ethylene, i.e. when the second and more 14 CO molecules insert into the polymer chain. Catalyst activity and the number of AC (in the range of 1.5 to 6% of Ni content) decrease with polymerization time. For both catalysts the values of the propagation rate constant are maximum at short polymerization time (5 to 15 min) and equal to (3 ± 0.8). 10 3 L/(mol. s) at 65°C.