Kinetic studies on a Ziegler catalyst system

Abstract

Measurements have been made on the kinetics of the polymerization of ethylene using Ziegler‐type catalysts made from zine di‐n‐butyl and titanium tetrchloride in hydrocarbon solvents. The rate of polymerization was proportional to the square of the ethylene pressure. At catalyst ratios (the molar ratio of zine butyl to titanium tetrachoride in the reaction mixture) less than 0.5, an initial, fast polymerzation was followed by a slower but more persistent polymerization. Both processes increased in velocity with increasing ratio up to 0.5; above this ratio the fast process was not observed while the rate of the slower one decreased with increasing ratio and was very small at unit ratio. At higher ratios the rate increased again as though to reach a limiting value when a very large excess of zine butyl was used. It has not been possible to devise more than speculative interpretations of these results. They suggest that at ratios greater than unity the reaction may be completed and that the chain initiation step takes place between zine butyl and ethylene, both adsorbed equilibrium‐wise onto the solid, reduced titanium choloride. It is not yet known whether propagation of polymerization occurs along the catalyst surface or at single sites on the surface. If the former is the case and the mobile propagation center is an ion‐pair, the hydrocarbon end being negative and the positive charge lying in the surface, the mobility of this latter charge may limit the rate of propagation. It is possible to explain some of the results obtained most easily from these ideas.

Catalytic Olefin Polymerization

“…The combinations of the two components which are active in ethylene polymerization are numberless [60,02]. As organometallic compounds, they have been used, in mixture with TiCl 4 or TiCI 3 , alkyl or hydride derivatives of AI, Li [63], Na [64], K [65], Zn [66,67], Cd [68], Ga [69], and B [70].…”

The Organic Chemistry of Titanium.

“…Ethylene is polymerized under the influence of titanium (IV) and tetrabutylzine at a rate which is proportional to the square of the ethylene concentration (132). Orzechowski (303) has found that the most efficient catalyst ratio for a mixture of titanium ( 7) chloride and isobutylaluminum is between 1.4 and 2.8 (aluminum: titanium).…”

Kinetic studies with a Ziegler catalyst system in the gaseous phase

“…For example, Feilchenfeld & Jeselson (1959), in studies with the active complex obtained from aluminium triethyl and titanium tetrachloride, concluded th a t the polymerization is first order with respect to ethylene and to titanium tetrachloride if the alkylating agent is in excess. McGowan & Ford (1958) and Gilchrist (1959) found th at ethylene polymerization with a catalyst composed of titanium tetrachloride and an excess of either lithium butyl or zinc dibutyl was first order in metal halide and second order in monomer. Ludlum, Anderson & Ashby (1958) have investigated the polymerization of ethylene using four different alkylating agents together with titanium tetrachloride as catalysts.…”

“…The value of this ratio depended upon the nature of the metal alkyl. Kinetic measurements using other a-olefins and diolefins have been made by N atta (1959( ), by N atta & Pasquon (1959 and by Gaylord,Kwei & Mark (i960). These authors have investigated the effects of solvent, temperature and metal alkyl/metal halide ratio on the rates of polymerization and on the pro perties of the polymers.…”