The functions of crystallizable ethylene-propylene copolymers in the formation of multiple phase morphology of high impact polypropylene

The functions of crystallizable ethylene-propylene copolymers in the formation of multiple phase morphology of high impact polypropylene (hiPP) were studied by solvent extraction fractionation, transmission electron microscopy (TEM), selected area electron diffraction (SAED), nuclear magnetic resonance (¹³C-NMR), and selected reblending of different fractions of hiPP. The results indicate that hiPP contains, in addition to polypropylene (PP) and amorphous ethylene-propylene random copolymer (EPR) as well as a small amount of polyethylene (PE), a series of crystallizable ethylene-propylene copolymers. The crystallizable ethylene-propylene copolymers can be further divided into ethylene-propylene segmented copolymer (PE-s-PP) with a short sequence length of PE and PP segments, and ethylene-propylene block copolymer (PE-b-PP) with a long sequence length of PE and PP blocks. PE-s-PP and PE-b-PP participate differently in the formation of multilayered core-shell structure of the dispersed phase in hiPP. PE-s-PP (like PE) constructs inner core, PE-b-PP forms outer shell, while intermediate layer is resulted from EPR. The main reason of the different functions of the crystallizable ethylene-propylene copolymers is due to their different compatibility with the PP matrix.