Self-Assembly of Nonfrustrated ABCBA Linear Pentablock Terpolymers

The effects of compositions, interaction parameters, and number of blocks on the self-assembly of nonfrustrated ABCBA linear pentablock terpolymer melts are investigated and compared with the corresponding ABC linear triblock terpolymers using the self-consistent field theory. For the case of symmetric interaction parameters (chi N-AB = chi N-BC) and majority B-blocks, both ABC triblocks and ABCBA pentablocks can form intriguing A- and C-domains embedded in the B-matrix. While these morphologies persist in the ABC systems when the segregation strength is decreased, the A blocks tend to mix with the B blocks in the ABCBA pentablocks due to the chain topology, resulting in the formation of C-domains embedded in the AB-mixed matrix. Different phase behavior is observed for the case of asymmetric interaction parameters (chi N-AB < chi N-BC). Aside from the core-shell type structures, a number of morphologies arise due to the separation between C and AB-mixed domains in ABCBA pentablock copolymers. The theoretical results not only capture the self-assembling behavior of poly(isoprene-b-styrene-b-ethylene oxide-b-styrene-b-isoprene) pentablocks, but also provide concrete suggestions for designing diverse microstructures in the linear ABC-type terpolymers.