Propylene polymerization is carried out with a C-2-symmetric metallocene catalyst of rac Et(Ind)(2)ZrCl2/MAO at 40 degrees C in the presence of a cyclo-triene of trans, trans, cis-1,5,9-cyclododecatriene ((E, E, Z)-CDT). Comonomer incorporations are rather low (<0.10 mol%). However, it is shown for the first time that the comonomer causes a noticeable increase in poly propylene isotacticity (>7% in [mmmm]). (E, E, Z)-CDT is speculated to coordinate to the metal center forming comonomer-complexed active sites in charge of the entire polymerization reaction with decreased activity however increased propylene enantiomorphic selectivity.