Stabilizing DG, DD, and DP Bicontinuous Network Phases in Pure AB-Type Block Copolymers beyond Relieving Packing Frustration

The spontaneous formation of bicontinuous networks in block copolymers is attractive for both fundamental research and technological applications. However, due to the packing frustration associated with the nonuniformities of interfacial curvature and domain size, obtaining network structures beyond a double-gyroid still presents a great challenge. Herein, we demonstrate that a delicately designed A′(A″B)5 miktoarm star copolymer can stabilize double-diamond and double-primitive network phases besides double-gyroid. A number of sophisticated mechanisms for stabilizing the networks are revealed, including the amplified effect of spontaneous curvature originating from the cone shape of A-blocks, effect of combinatorial entropy associated with multiple A″B arms, and the effect of local segregation between the long A′ and short A″-blocks. Under the synergistic effect of these three sophisticated mechanisms, the concentrations of A′ and A″ blocks in the nodes and struts are regulated by tuning the architectural parameters, thus controlling the sizes of the node and strut to match the geometry of various network structures. In brief, the A′(A″B)5 copolymer with ingeniously tailored architectures can adopt two largely different forms of conformations to adapt to the local geometries of the node and strut of these three bicontinuous network phases, thus stabilizing them. Abiding by these mechanisms, more AB-type architectures can be rationally devised to realize different networks. To the best of our knowledge, this is the first time we report three bicontinuous network phases in the phase diagram of neat AB-type block copolymer melts.