A kinetic mechanism for the heterogeneous stereospecific polymerization of propylene

• Published in: Journal of polymer science 1960-10, Vol.46 (148), p.375-381
• Main Author: Saltman, William M.
• Format: Article
• Language: English
• ISSN: 0022-3832; 1542-6238
• DOI: 10.1002/pol.1960.1204614807

A theoretical examination of the kinetics of the polymerization of propylene with Al(C2H5)3–TiCl3 has been made. A reaction scheme is proposed which, with the use of adsorption equations, allows the calculation of propagation and termination rates. The calculated degree of polymerization is in semiquantitative agreement with the experimental results reported by Natta and indicates that a single termination reaction can account for the major part of the experimental results. The role of the solid is still somewhat obscure but it probably takes part in a second termination reaction. Propagation is due to the growth of the adsorbed aluminum alkyl, and the experimental propagation rate indicates that polymerization proceeds when the alkyl, on the almost completely covered surface, reacts with monomer which may be adsorbed or not. Before termination occurs, the now long‐chain aluminum alkyl is desorbed and may exist free in solution. Termination occurs when this alkyl is readsorbed on or reacts with a second type of surface site which is active only for termination. The overall process is akin to those proposed for enzyme reactions.