Hydrogen bonding induced microphase and macrophase separations in binary block copolymer blends

This study investigated the macrophase and microphase transitions of blends comprising polystyrene -block-poly (ethylene oxide) (PS-b-PEO) and polystyrene-block-poly(acrylic acid) (PS-b-PAA). PEO and PAA molecules formed hydrogen bonds that enabled the two block copolymers to organize into a single microphase-separated morphology composed of two PS block chains in a common PS microdomain and PEO and PAA block chains in a coexisting PEO/PAA microdomain. Increasing temperature weakened the hydrogen-bonding interaction through the formation of PAA monomers and anhydride, causing the blends to macrophase separate into PS-b-PEO-rich and PS-b-PAA-rich phases. Further increasing the temperature weakened the repulsive interactions between both the PS and PEO segments and the PS and PAA segments, inducing order-to-disorder transitions in the PS-b-PEO-rich and PS-b-PAA-rich phases. However, the increasing repulsive interaction between the PEO and PAA seg-ments with increasing temperature prevented the blends from forming an isotropic phase. The unique phase transformation of each block copolymer in the blend with an upper critical ordering transition (UCOT)-type interaction parameter, which caused the formation of a lower-critical-solution-temperature-type phase diagram, was attributed to the hydrogen-bonding interaction between PEO and PAA, which outweighed the UCOT be-haviors of PS-b-PEO and PS-b-PAA and reversed the phase behaviors of their blends.