Copolymer Distribution in Core–Shell Rubber Particles in High-Impact Polypropylene Investigated by Atomic Force Microscopy–Infrared

High-impact polypropylene (HIPP) is an important and industrially relevant material with a complex morphological structure. In this paper, two commercial resins with similar rubber contents are investigated by atomic force microscopy–infrared to determine in situ ethylene contents in the rubber and core phases, and then, in conjunction with chain composition information obtained ex situ, distribution of the component copolymers in these phases is elucidated. The rubber phases in both alloys comprise ethylene–propylene rubber and a little amount of ethylene–propylene-segmented copolymer (EsP). The core phases in the two resins, although both rich in propylene and of similar ethylene content, exhibit very different compositions and structures. The core in one resin is composed of EsP, the ethylene segments of which can crystallize, and the ethylene–propylene block copolymer (EbP) component forms an outer shell for the rubber particle, showing a typical morphology of HIPP. The core in the other resin comprises a substantial amount of polypropylene (PP) homopolymer in addition to EsP and EbP, which leads to PP crystallinity in the core, an unusual structure that contributes to the superior rigidity–toughness balance of the material. The unique phase composition can be attributed to the more balanced structure of the EbP component.