Kinetics of hexene-1 polymerization using [(N,N'-diisopropylbenzene)-2,3-(1,8-napthyl)-1,4-diazabutadiene] dibromonickel/methylaluminoxane catalyst system

Abstract

Kinetics of hexene-1 polymerization was investigated using [(N,N'-diisopropylbenzene)2,3-(1,8-napthly)-1,4-diazabutadiene]dibromonickel/methylaluminoxane catalyst. Experiments were performed at varying catalyst and monomer concentrations in the temperature range of -10 to 35 °C. First order time-conversion plot shows a downward curvature at temperatures of 20 °C and 35 °C indicating the presence of finite termination reactions. A nonlinear plot of degree of polymerization (P_n) with respect to conversion indicates occurrence of transfer reactions and slow initiation. The experimental molar masses are higher than predicted, which implies that a fraction of catalyst species could not be activated or is deactivated at the early stages of the reactions. The efficiency of the catalyst (Cat_eff) varies from 0.77 to 0.89. The observed polydispersity of the poly(hexene-1) s is in the range of 1.18-1.48. The reaction order was found to be 1.11 with respect to catalyst. The Arrhenius plot obtained using the overall propagation rate constant, k_p, at five different temperatures (-10, 0, 10, 20, and 35 °C) was found to be linear with an activation energy, E_a = 4.3 kcal/mol. Based on the results presented it is concluded that the polymerization of hexene-1 under the above-mentioned conditions shows significant deviation from ideal "living" behavior.