High selectivity in polymerization of (Z)-1,3-pentadiene, with the CpTiCl3-MAO catalytic system, generated by backbiting coordinations of the growing polydienyl chain.

Polymer microstructures obtained by copolymerizations of (Z)-1,3-pentadiene with ethene, conducted at different temperatures by the CpTiCl3-MAO catalytic system, have been characterized by detailed 13C NMR analyses. The observed microstructures indicate an essential role of the backbiting of the allyl-terminated growing chain on the occurrence of 1,2 syndiotactic and 1,4-cis high selectivities, which are observed for (Z)-1,3-pentadiene homopolymerizations at low and high temperatures, respectively. Molecular modeling studies suggest that the occurrence of 1,2-syndio and 1,4-cis stereoselectivities would be determined by the steric constrain (and stereorigidity) associated with the maintenance, in monomer bound intermediates, of the backbiting coordination of syn and anti allyl-terminated growing chains, respectively.