Impact polypropylene copolymers containing multifold H-shape long-chain-branching structures: Effect on dielectric and electrical properties

This paper discusses the dielectric and electrical properties of novel impact polypropylene copolymers containing multifold H-shape long-chain-branching structures (LCB-IPCs), i.e. PP-H-PP, PP-H-EPC (EP copolymer), and EPC-H-EPC. Dielectric spectroscopy study indicates that the LCB structures tend to decrease the dielectric constant of IPC increased from that of net PP due to EPC alloying. Electron trap distribution study reveals that the LCB structures have the effect of deepening the electron traps of IPC shallowed from those of net PP by EPC alloying. Similar effect of LCB structures extends to electrical breakdown properties. Compared to LCB structure-free pristine IPC, which is reduced on electrical breakdown strength under both AC and DC electrical voltage as compared to net PP, LCB-IPCs are on the contrary measured continuously increased breakdown strengths in both occasions. The improvements in electrical properties of LCB-IPCs are mainly attributed to the crystalline morphology alterations, i.e. decreasing in spherulite size and increasing in spherilite density, due to PP-H-PP structure exercising effective nucleation for PP crystallization.