A kinetic study of ziegler‐natta propylene polymerization

The kinetics of the propylene polymerization with TiCl3‐AlEt3 has been investigated in the temperature range (30‐70°C.), the pressure range of propylene (100‐700 mm. Hg), and the concentration range of the catalysts (2 g. TiCl3/liter, [A]/[Ti] = 0.4‐3.0). The polymerization rate R increases rapidly with the polymerization time t at first (stage I), which is followed by a gradual decrease to the stationary value Roo, (stage II). The kinetic behavior in stage I in the case when propylene is introduced after the addition of AlEt3 is expressed by and that in the case when propylene is introduced before the addition of AlEt3 is expressed by The kinetic behavior in stage II, which is independent of the above procedure, is expressed by where R∞ is the stationary rate represented by and Ro a constant. The activation energies are E1 = 15, E2 = 17, Et3 = 2‐3, E3″ = 12, and EP = 10 kcal./mole, respectively. The heat of adsorption of AlEt3 was obtained as 12 kcal./ mole from the temperature dependence of K. Stage I is explained on the basis of the formation of polymerization centers from Al2Et6 and a propylene monomer on the surface of TiCl3. Stage II is attributed to an irreversible deactivation of the polymerization centers localized on unstable surface sites due mainly to a spontaneous process and partially to a propylene monomer (or polymer) attack.