Abstract:
Microgravimetric measurements have been used to follow the polymerization of ethylene and propylene on a supported Ziegler catalyst prepared by treatment of MgO with TlCl4 followed by AlEt3. Polymerization between 273 and 320 K obeyed the parabolic law, with activation energies close to those for monomer permeation through the corresponding polymer. These observations, together with a first order dependence on monomer pressure, were taken to indicate that monomer permeation through an encapsulating polymer film was the rate determining step. Quantitative considerations suggest that the encapsulated material consists of agglomerates of MgO crystallites, such that the effective catalyst area is two orders of magnitude less than the B.E.T. area of the MgO.
