The self-assembly of block copolymers (BCPs) is a useful method to achieve highly-ordered, nanoscale structures, such as lamellae, cylinders, and gyroids, which find use in many fields, such as lithography, separation, and catalysis. For membrane applications, the cylinder morphology has been widely studied and utilized because it is easy to synthesize cylinder-forming BCPs. However, it is challenging to align cylindrical channels that continuously extend through the entire thickness of the BCP film. Gyroid structures, on the other hand, can form continuous channels throughout the entire BCP film without the need of alignment. Therefore, it is of great interest to use gyroid structures for membrane applications. Because the gyroid morphology exists in a narrow window of the BCP phase diagram, it is necessary to have precise control over the synthesis of BCPs for making gyroids. By the combination of living anionic polymerization and organocatalytic ring-opening polymerization (ROP), the precise control over the composition of silicon-containing BCP, poly(trimethylsilylstyrene-<i>b</i>-lactide) (PTMSS-<i>b</i>-PLA), has been achieved. First, the hydroxyl-terminated polytrimethylsilylstyrene, PTMSS-OH, is synthesized by living anionic polymerization and used as the macro-initiator. Then, the polylactide, which is degradable in basic solution, is grown from the PTMSS-OH block by organocatalytic ROP. The gyroid morphology of PTMSS-b-PLA has been confirmed by small angle X-ray scattering and scanning electron microscopy (SEM) after the removal of PLA block. The Si-containing porous gyroid film has potential uses in fabricating highly selective membranes for various applications, such as water purification and gas separation.

Gyroids with an organosilicon block for membrane applications

2019 Spring National Meeting

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