Unique Phase Behavior of Inverse Tapered Block Copolymers: Self Consistent Field Theory and Molecular Dynamics Simulations

Using theory and simulation, we study the microphasese-parated structures of inverse tapered block copolymers. These are AB block copolymers with a gradient region inserted between the pure A and B blocks that smoothly changes in composition from B to A, with the B side of the taper bonded to the pure A block. Tapering is a means to increase miscibility between polymer blocks, and by controlling the length of the taper, the phase behavior and domain spacing can be adjusted. In contrast to better known ABAB tetrablock copolymers that also have four alternating A-rich and B-rich regions, here the intermediate region has a partially mixed composition, promoting relatively diblock-like behavior for shorter inverse tapers or low segregation strength but unique behavior as a function of increasing, segregation strength for some systems. In particular, for systems in which 50% of the backbone is the taper, the larger of the two pure end blocks-composed of the overall majority component-can phase separate analogously to the minority component of a diblock copolymer, creating cylinder and network phases in which the majority, component's pure block is the minority phase in a matrix of a relatively disordered mixture of the tapered region and the minority component's pure block.