Crystallization Behavior And Mechanical Properties Of Regiodefective, Highly Stereoregular Isotactic Polypropylene: Effect Of Regiodefects Versus Stereodefects And Influence Of The Molecular Mass

Highly isotactic polypropylene samples, containing a very low amount of rr stereodefects (0.1−0.2%) and slightly higher concentration of defects of regioregularity (0.8−0.9% of 2,1 erythro units), with different molecular masses have been prepared with an isospecific but not fully regioselective metallocene catalyst. The effects of the presence of rr defects and of 2,1 regiodefects and the effect of the molecular mass on the mechanical properties and crystallization behavior of polypropylene have been analyzed. Samples containing 2,1 regiodefects are very stiff and much more fragile than the samples containing only rr stereodefects. The presence of rr defects, even for low concentrations, produces instead increase of ductility and improvement of drawability at room temperature. The different effect of stereo- and regiodefects is probably related to their different levels of inclusion inside the crystalline phase. The uniform inclusion of rr defects in the crystals makes the stereodefective and regioregula...