Kinetics of the ethylene‐propylene copolymerization

The results obtained from a systematic kinetic study of ethylene‐propylene copolymerization in the presence of catalysts prepared from Al(C6H13)3 and VCl4, already reported are briefly summarized. The considerable increase of the overall copolymerization rate, observed with the increase of the ratio of ethylene to propylene in the reacting liquid phase, cannot be explained only on the basis of the values of the kinetic constants of propagation, but it is also necessary to admit a variation in the concentration of the number of growing chains. Some experimental evidences are indicated proving this hypothesis. This result cannot be extended to the ethylene‐propylene copolymerization in the presence of other catalytic systems acting through an anionic co‐ordinated mechanism, for which the ratio between the rates of ethylene and propylene homopolymerization is very close to the value of the reactivity ratio of ethylene. Finally, an equation is proposed which interprets, to a good approximation, the values of the overall rate of the copolymerization process in the presence of the catalytic system Al(C6H13)3—VCl4.