Visualizing phase separation in polystyrene/polystyrene homo‐IPNs via sulfonation

BACKGROUND: Polystyrene/polystyrene (PS/PS) interpenetrating polymer networks (IPNs) represent ideal homo‐IPNs. Whether phase separation occurs in this system has been a long‐standing problem, which is closely related to the self‐organization mechanism in IPN formation and is important to the exploration of new polymer morphologies and properties by topological isomerism. RESULTS: A series of bead samples of PS/PS sequential IPNs with the same nominal divinylbenzene contents were synthesized by suspension polymerization, followed by sulfonation. Scanning electron micrographs and energy‐dispersive X‐ray mapping show unique distinctive topography on both surfaces and fractured surfaces and large heterogeneity in sulfonation of the PS/PS IPN beads, which for the first time provide visual evidence for dual‐phase continuity in PS/PS IPNs. CONCLUSION: The phase separation behavior is proposed to be due to hydrodynamic screening, architectural asymmetry and excluded volume interactions between network I and the precursor chains of network II. This is considered to represent pure IPN effects in sequential formation and may shed light on the general constitution mechanism and molecular design of IPN materials. Copyright © 2009 Society of Chemical Industry