Topological and End-Functionalized Effects on Controlled Self-Assembly of High-χ Block Copolymers for Network Phase Formation

This work aims to examine the effects of topology and end-group chemistry on the self-assembly of high-χ block copolymers (BCPs), specially, polystyrene-block-polydimethylsiloxane (PS-b-PDMS). Lamellae-forming diblock, star-blocks and end-tethered diblock functionalized with hydroxyl group at the end of PDMS block are synthesized for self-assembly. By using PS-selective solvents for solution casting, a variety of self-assembled phases, especially metastable network phases, can be formed at which the corresponding phase behaviors can be enriched by tuning the solvent evaporation for solution casting; that is referred as controlled self-assembly. In contrast to diblocks with linear architecture, the formation of network phases can be easily acquired by using PS-selective solvents with various selectivity when star-blocks are used. Lowering the evaporation rate for controlled self-assembly of the star-blocks enriches the forming network phases, giving double gyroid, double diamond and even FK-like network phase with alternating three- and four-strut nodes. Similar outcomes for the phase behaviors can also be observed in the self-assembly of end-tethered PS-b-PDMS due to the alleviation of packing frustration from hydrogen bonding association. Accordingly, controlled self-assembly of high-χ BCPs demonstrates twin effects on the phase behaviors of topological and end-functionalized BCPs, giving an easy access to acquire a variety of network phases.