Chain microstructure of two highly impact polypropylene resins with good balance between stiffness and toughness

For highly impact polypropylene (HIPP), a good balance between stiffness and toughness has attracted much attention from both industrial and academic research. Herein, two HIPP resins (A and B) with different ethylene contents and impact resistances especially at low temperatures are investigated. Their chain microstructure is studied by combining preparative temperature rising elution fractionation (P-TREF) with multiple characterization techniques such as high-temperature gel permeation chromatography (HT-GPC), Fourier transform infrared (FTIR) spectroscopy, 13C nuclear magnetic resonance (13C NMR), wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), rheometer, and thermal fractionation. Both samples are mainly composed of four portions: amorphous ethylene−propylene random copolymer (EPR), ethylene−propylene (EP) segmented and blocky copolymer, and isotactic polypropylene homopolymer. Sample A contains ~30 wt% EPR fractions eluted at 35 °C, ~9 wt% EP segmented and blocky copolymers eluted at 80–100 °C, and ~19 wt% highly isotactic polypropylene fractions eluted at 125–140 °C, which are higher than the contents of corresponding fractions in sample B. Moreover, most fractions of sample A have higher molecular weights than the corresponding fractions of sample B. The contribution of different components to stiffness and toughness is also discussed. The excellent impact resistance of sample A is demonstrated from the perspective of chain microstructure.