Side Chain Induced Morphology Changes in Brush-Linear Diblock Copolymers

Brush-linear block copolymers represent an interesting class of materials as they exhibit complex phase morphology with characteristics of both coil-coil and rod-coil block copolymers. In this study, we investigate the self-assembly of brush-linear block copolymers where both the brush side chain density and chain length are systematically varied. A poly(pentafluorophenyl acrylate-b-styrene) (PPFPA-b-PS) linear diblock copolymer is first prepared as the precursor polymer. The PPFPA block is then reacted with amine-functionalized poly(ethylene glycol) (PEG) to create brush-linear type block copolymers of the chain structure (PPFPA-g-PEG)-b-PS. Different degrees of PEG substitution are conducted, and the resulting brush-linear block copolymers are examined to determine their bulk morphologies by small-angle X-ray scattering (SAXS). As the degree of PEG side-chain substitution increases, block copolymer morphology is found to transition from lamellae to a newly formed frustrated lamellae then to hexagonally-packed cylinder. Furthermore, when PEG chains of longer chain length are used, the same morphology transition is again observed while these transitions occur at even lower degrees of side-chain substitution.