Hajime Kishi

ABSTRACT A modifier for epoxy resins with a long‐chain aliphatic structure and imide groups is proposed. The compatibility of the modifier with epoxy resins and the phase‐separated structure of the cured resins are evaluated. The blends of the modifier and the epoxy resin exhibit an upper critical solution temperature‐type phase diagram. In addition, the cloud point for the modifier with biphenyl‐type epoxy resins is lower than that with bisphenol A‐type epoxy resins. The good compatibility between the modifier and the epoxy resin is suggested to be due to charge‐transfer interactions as determined by ultraviolet–visible spectroscopy. The cured epoxy resins containing the modifier form phase‐separated structures. In particular, the cured resin using the biphenyl‐type epoxy resin exhibits submicron island phases of 300 nm or less, as determined by transmission electron microscopy. The addition of the modifier reduces the storage modulus of the cured epoxy resin by approximately 500 MPa while maintaining the glass transition temperature.

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.

Abstract Amorphous polymer/crystalline polymer blends can be prepared via the simultaneous polymerization of polymethacrylate/polyurethane combinations. The relationship between higher order structures and fracture mechanisms in these blends must be uncovered to elucidate the source of the increased fracture toughness of such materials. The present work involves the production of blended polymethacrylate/polyurethane and assess the internal structures of these specimens using optical and electron microscopy. These observations reveal the presence of both spherulites and elastomeric phases. The spherulites consisting of the polyurethane and are several micrometers in diameter whereas the phase‐separated polyurethane elastomeric domains are approximately 100 nm in size. Multiple cracks, crack bridging and plastic deformation around the precrack tips of loaded specimens are evidently responsible for the increased toughness of these blends. The former two phenomena are attributed to the presence of spherulites while the plastic deformation of the methacrylate matrix is ascribed to cavitation of the polyurethane elastomeric phases in response to loading.