Ethylene–propylene copolymerization initiated with solubilized Ziegler–Natta macromolecular complexes. I. Determination of kinetic parameters

Copolymerization of ethylene with propylene (E–P) was initiated with soluble polystyrene –butadiene–Li/TiCl₄ complexes in toluene leading to vinylic-olefinic based block copolymers. The activity of the system was measured at a constant ratio r = Li/Ti for different feed compositions. From measurements of the amount of copolymers produced, a direct determination of the efficiency of the catalytic system was made. This efficiency was found to be close to that obtained for homopolymerizations of C₂H₄ and C₃H₆ initiated with the same catalytic complex (? 80% with respect to the concentration of “carbon-titanium” bonds). Both the measured values of the efficiency and the determination of the molar masses of the polyolefinic block are consistent with a living character of the system involved in the E–P copolymerization. In such conditions well-defined linear [styrene]-b-[ethylene-co-propylene] copolymers were obtained. Furthermore, ¹³C NMR analyses allowed determination of the comonomer reactivity ratios, the values of which indicate an E–P random copolymerization. From both these values and those of the absolute rate constants of propagation determined for the homopolymerization of C₂H₄ and C₃H₆ initiated with the same catalytic system, the absolute rate constants of cross-propagation were deduced.