Search

This study of Al–TiCl4 catalysts for olefin polymerization continues work reported in preceding papers but with the use of aluminum wire under constant pressures. The use of aluminum having a very small surface area was convenient for the kinetic study of the reaction mechanism. The reaction time is divided into four periods. The first and second are connected with active-center formation and are considered to be a kind of induction period. The third is a stationary period in which the rate is proportional to the square of pressure and the activation energy is ca. 16 kcal./mole. In the fourth period the rate is proportional to pressure and decreases gradually owing to a rate-controlling diffusion step through the polymer layer produced. A kinetic consideration is proposed and a reaction scheme formulated for initiation, propagation, transfer, and termination. An ethylene-propylene copolymerization study was also carried out, and lead to the supposition of a cationic mechanism in respect to the present type of polymerization.