The mechanism of Ziegler-Natta polymerization of 4-methyl-1,3-pentadiene: a theoretical study of the coordination step

The coordination step of l-2 homopolymerization of 4-methyl- 1,3-pentadiene in presence of Ziegler-Natta initiators is discussed on the basis of ab initio computations. The results show that, as for l-4 homopolymerizations, the coordination of the incoming monomer requires a substantial rearrangement of the ending unit, whose coordination mode changes from the n’-allylic type to the n’-a one. This step, most probably the rate-determining one, appears to be easier for 4-methyl-1,3- pentadiene than for butadiene or isoprene homopolymerization, in agreement with the observed homopolymerization rates.