It has been well known that the phase boundaries of AB-type block copolymers can be largely deflected by designing their asymmetric architectures to regulate the stable regions of various ordered phases in a large range. One of the simplest asymmetric architecture is AB${}_n$ miktoarm star, of which the spherical and cylindrical regions are significantly enlarged by the deflections of the phase boundaries toward large volume fraction of A-block. Accordingly, we design a symmetric ABC-type pentablock terpolymer by branching B-blocks, i.e. connecting one of the B-arms of a pair of miktoarm star copolymers AB${}_2$ and CB${}_2$ together. This symmetric pentablock terpolymer is composed of two equal A and C blocks tethered on a B-chain. We investigate the self-assembly behaviors of this terpolymer using self-consistent field theory, focusing on the control of the length ratio of the middle B-block to the total B-blocks on the regions of alternating spherical, cylindrical and gyroid phases. It is predicted that the three phase regions are successfully regulated in a large range by the architectural parameter, which are accompanied by a lot of interesting phase behaviors. For instance, an unusual order-order transition from the spherical phase to the gyroid phase with the absence of the cylindrical phase is determined. Our results reveal that these interesting phase behaviors result from three sophisticated effects including the branching effect on the spontaneous curvature, the released packing frustration from different B-blocks and the stretched bridging middle B-block.

众所周知，AB 型嵌段共聚物的相边界可以通过设计它们的不对称结构来在很大范围内调节各种有序相的稳定区域，从而在很大程度上偏转。最简单的非对称架构之一是 AB${}_n$miktoarm 星，其中的球形和圆柱形区域因相界向 A 块的大体积分数的偏转而显着扩大。因此，我们通过支化 B 嵌段设计了一种对称的 ABC 型五嵌段三元共聚物，即连接一对 miktoarm 星形共聚物 AB 的一个 B 臂${}_2$ 和CB${}_2$一起。这种对称的五嵌段三元共聚物由连接在 B 链上的两个相等的 A 和 C 嵌段组成。我们使用自洽场理论研究了这种三元共聚物的自组装行为，重点是控制交替的球形、圆柱形和陀螺相区域上中间 B 嵌段与总 B 嵌段的长度比。据预测，三相区域被建筑参数成功地在大范围内调节，并伴随着许多有趣的相行为。例如，确定了从球形相到没有圆柱相的陀螺相的异常有序过渡。