Influence of catalyst depletion or deactivation on polymerization kinetics

Kinetic models based on the time dependence of the deactivation of catalyst sites have been fitted to data on reaction kinetics taken from the literature for polymerization of various olefins on a series of ionic and coordinate catalysts (both homogeneous and heterogeneous) for a variety of polymerization conditions. In clean coordinate polymerization systems where termination is unimportant, the propagation reaction plays a major role and is influenced by the number of active catalyst sites. The number of sites remains constant in some catalysts but varies in most. First‐order deactivation of catalyst sites leads to dead‐end kinetics similar to that described by Tobolsky for free‐radical polymerization with catalyst depletion by first‐order decomposition. Second‐order deactivation leads to kinetics linear in the logarithm of time. In heterogeneous polymerization, it is difficult to find a physical model for interaction of isolated sites required for higher‐order deactivation. The experimental data are fitted equally well by a mixed‐order model assuming sites of different stability exhibiting first‐order deactivation. At low conversions, the models are difficult to fit to experimental data in which monomer concentration is varing. Further experiments are required to test the models, obtain exact values for rates constants, and determine the influence of catalyst deactivation on molecular weight and molecular weight distribution.