THE MECHANISM OF ZIEGLER-NATTA POLYMERIZATION OF 4-METHYL-1,3-PENTADIENE - A THEORETICAL-STUDY OF THE COORDINATION STEP

The coordination step of 1-2 homopolymerization of 4-methyl-1,3-pentad iene in presence of Ziegler-Natta initiators is discussed on the basis of ab initio computations. The results show that, as for 1-4 homopoly merizations, the coordination of the incoming monomer requires a subst antial rearrangement of the ending unit, whose coordination mode chang es from the eta(3)-allylic type to the eta(1)-sigma one. This step, mo st probably the rate-determining one, appears to be easier for 4-methy l-1,3-pentadiene than for butadiene or isoprene homopolymerization, in agreement with the observed homopolymerization rates. (C) 1998 Elsevi er Science B.V.