Phase Transformations Involving Network Phases in ISO Triblock Copolymer−Homopolymer Blends

Abstract

Poly(isoprene-b-styrene-b-ethylene oxide) (ISO) triblock copolymers were blended with poly(styrene) and poly(isoprene) homopolymers at compositions close to those previously shown to produce triply periodic, multiply continuous network phases. Homopolymer molecular weights were approximately equal to the corresponding block molecular weights, and homopolymer concentrations up to 21 vol % were explored without evidence of phase separation. Three triply periodic network phases were identified: a core−shell double gyroid (Q230, Ia3d space group symmetry), an orthorhombic network (O70, Fddd space group symmetry), and an alternating gyroid (Q214, I4132 space group symmetry). Tuning the overall composition by adding homopolymer resulted in systematic phase transitions between the Q230 and O70 networks and between the Q214 and O70 networks. In addition, doping with both poly(styrene) and poly(isoprene) homopolymer induced transitions from three-domain lamellae (LAM3) to the O70 network phase. In general, phase...