Effect of Polymerization‐Induced Phase Separation on Flame Retardancy of Cyanate Ester/Polyethersulfone Blends and Thermal Conductivity of Composites With Graphite Fillers

ABSTRACT The effect of polyethersulfone (PES) blends on the flame retardancy of dicyanate ester of bisphenol E (DCBE) cured resin was investigated. The DCBE/15 wt% PES cured blends formed co‐continuous phase structures by polymerization‐induced phase separation. When heating up to 200°C for curing, varying the temperature ramp rate was found to affect the size and glass‐transition temperature of domains of the two phases in the blends. The self‐extinguishing time was influenced by the phase domain size, with the highest flame retardancy being obtained when the width of the PES‐rich domains was around 3 μm. DCBE/15wt%PES/graphite filler composites with a co‐continuous phase structure and selectively localized graphite filler exhibited a higher thermal conductivity than DCBE/graphite filler composites without phase separation. The small amount of graphite filler was selectively localized in the cyanate‐rich continuous phases so that the graphite particles had more opportunities to contact each other within the micrometer‐sized templates. Due to their high flame retardancy and thermal conductivity, cured DCBE/PES polymer blends with a small amount of graphite filler offer great potential for applications in the aerospace industry.