A novel double-percolation structural conductive polymer composite based on epoxy/polyetherimide/carbon black was prepared for the first time. The electrical property, phase structure of the composite and the selective distribution of carbon black were investigated. The results show that a reaction-induced phase separation between epoxy and polyetherimide can be observed in epoxy/polyetherimide/carbon black composites. In the blend with 16 wt% polyetherimide, polyetherimide phase changes from a dispersed phase to a three-dimensionally continuous phase, while epoxy converts to a globular dispersed phase. The selective distribution of carbon black in the blends is that almost all carbon black particles are located in polyetherimide phase. Accordingly, a double-percolation structure is formed when carbon black content comes to the percolation threshold in polyetherimide phase. In fact, the percolation threshold of carbon black reduces to 0.5 wt% in the blend with 16 wt% polyetherimide.

Carbon nanotubes (CNTs) selective dispersion and electrical properties of one kind of thermoplastic/thermosetting polymer composite consisting of polyetherimide (PEI) and epoxy resin (EP) were investigated. The results showed that, in the CNTs/EP/PEI composite, under control of thermodynamics, CNTs are preferably dispersed in PEI-rich phase, and an inverted phase structure is obtained with continuous PEI-rich phase and separated EP phase as globular shapes. And this microstructure helps to achieve a very low percolation threshold of 0.3wt% CNTs in the composite. The composites at CNTs contents over the percolation threshold, have a high dielectric constant of around 100, which first decreases slightly and the drop rapidly into a platform with increasing frequency from beginning.