On the importance of diffusion of cocatalyst molecules through heterogeneous ziegler/natta catalysts

The effect of different cocatalysts in slurry phase polyethylene production using a high active Ziegler/Natta catalyst precursor was studied under different polymerization start-up methods. The study revealed that diffusion of cocatalyst molecules through produced polymer to reach potential active sites inside the catalyst precursor particles is an important factor as was already suggested in Ref. [1]. Increasing the molecular dimensions of the cocatalyst molecules thus results in a decrease in the rate of activation of the catalyst precursor. It was shown that polymer powder morphology is strongly effected by the time necessary to reach maximum polymerization activity which depends not only on the method of polymerization start-up [1], but also on the nature of the cocatalyst. Cocatalyst diffusion inside catalyst precursor particles can also be a possible explanation for the development of cobweb [2] structures in polymer particles.