Morphology Evolution in the Early Stages of Olefin Polymerization pp. 3-30
Authors: (Joachim Loos, Xuejing Zheng and Peter C Thüne)
Abstract: The properties of olefin polymers greatly depend on their molecular microstructure, e.g. molecular weight and molecular weight distribution, comonomer content and composition. Significant progress has been made in understanding how catalyst activity, stereoselectivity, hydrogen response, etc., can be finely tuned by operating at the active centre level. In olefin polymerisation, the single polymer particle can be viewed as a microreactor, characterised by its own kinetics and balances of mass and energy. Apart from the nature of the active species, the microstructure of the final polymer is greatly affected by mass and heat transfer during the polymerisation, especially in the early stages of polymerisation. Our study focuses on the key parameters that affect the catalyst fragmentation and polymer particle morphology formation. Olefin homo- and copolymerisations (mainly based on propene) were carried out using MgCl2 supported Ziegler-Natta catalysts and silica supported metallocene/MAO catalysts under mild conditions and stopped at various yields. The surface and cross sectional morphology of the catalyst and polymer particles were characterised mainly by using microscopic techniques, enabling us to monitor the support fragmentation and polymer particle growth in the very early stages of the polymerisation.