Effects of Chain Topology on the Self-Assembly of AB-Type Block Copolymers

The effects of chain topology on the self-assembly of block copolymers are examined using an ABAT block copolymer, composed of an AB diblock copolymer with an extra A block tethered onto the B block, as a model system. The topology of the ABAT block copolymer is regulated by the tethering point, such that the block copolymer changes continuously from linear ABA triblock copolymer to A2B miktoarm star copolymer as the tethering position moves from the B end to the AB junction. The phase diagrams of ABAT copolymers of different tethering positions are constructed using the self-consistent field theory. The theoretical results reveal that the phase behavior of the system depends sensitively on the topology of the ABAT copolymers. In particular, a considerably wide stable region of the perforated lamellar (PL) phase is predicted for ABAT with proper tethering positions. The PL phase could even completely replaces the gyroid phase at relatively strong segregation. Furthermore, a large window of the hexagonally close-packed (hcp) spherical phase, as well as a direct transition from hcp to the cylindrical phase, is predicted. An analysis of the distributions of the different blocks reveals that the local segregation of the two different B blocks occurs to accommodate the topological constraints due to the chain architecture, which in turn regulates the local interfacial curvature and chain packing resulting in the different phase behaviors.