In this study, the viscoelastic phase separation process was studied further by time-resolved light scattering, differential scanning calorimetry, and scanning electron microscopy in the system of poly(ether imide)-modified bisphenol-A dicyanate. It was observed that the evolution time of phase structure and relaxation time of diffusion flow of the bisphenol-A dicyanate were similar with the phase diagram of curing conversion versus content of PEI. The results suggested that the viscoelastic phase separation was affected by the curing conversion of the system at the onset point of phase separation. (c) 2005 Wiley Periodicals, Inc.