Closed-Loop Phase Behavior of Block Copolymers in the Presence of Competitive Hydrogen-Bonding and Coulombic Interaction

The closed-loop phase behavior, where a lower disorder-to-order transition (LDOT) takes place first, followed by an upper order-to-disorder transition (UODT) upon heating, is seldom observed in block copolymers (BCPs). In this work, we prepared a model BCP, LiClO4-doped poly(ethylene oxide)-b-poly(tert-butyl acrylate-co-acrylic acid) (PEO-b-P(tBA-co-AA)), in which the hydrogen (H)-bonding between the PEO and AA units and the Coulombic interaction in salt-doped PEO block have opposite effects on the miscibility of BCPs. The relative strength of the H-bonding and Coulombic interaction can be easily tuned by the hydrolysis degree (DH) of the PtBA block and the amount of doped salt. Various phase behaviors are observed by changing relative strength of different forces. Especially, the closed-loop phase behavior can be achieved when H-bonding, Coulombic interaction, and mixing entropy reach a delicate balance.