Microstructure of two polypropylene homopolymers with improved impact properties

Two polypropylene homopolymers, samples A and B, synthesized with heterogeneous Ziegler–Natta catalysts, are studied in this work. Both samples show improved impact properties at low temperature than isotactic PP. Particularly, sample B exhibits better toughness, higher molecular weight and slight lower flexural properties than sample A. Then, these two samples were fractionated into six fractions via temperature rising dissolution fractionation, respectively. Both samples are mainly composed of fractions 4, 5 and 6, which were collected above 100 °C and have high isotacticity. On the one hand, the fractions of sample B have higher molecular weight than the corresponding fractions of sample A collected at the same temperatures. On the other hand, 13C NMR and DSC analyses of the fractions indicate clearly that fractions of sample B have lower isotacticity and crystallinity than the corresponding fractions of sample A. The above difference in microstructure between samples A and B should be the key factors resulting in their difference in mechanical properties finally. Both polypropylene homopolymers possibly become new type of impact PP.