Concurrent transformation of copolymer domain morphology induced by the order-disorder transition of comb block in supramolecular comb-coil block copolymer

An amphiphilic surfactant, dodecylbenzenesulfonic acid (DBSA), was complexed with poly(ethylene oxide) (PEO) block in poly(1,4-butadiene)-block-PEO (PB-b-PEO) through hydrogen bonding to yield a molecular architecture resembling comb-coil diblock copolymer. For the two binding fractions (x = 0.5 and 1.0 with x being the average number of DBSA molecules bound with one PEO monomer unit) studied, the supramolecular comb-coil diblocks exhibited a cylinder-within-lamellae morphology, where the PB cylindrical domains of ca. 28 nm in diameter embedded in the matrix consisting of the lamellar mesophase with the interlamellar distance of ca. 2.9 nm organized by the PEO(DBSA), comb blocks. The interdomain distance of PB cylinders was significantly smaller than the fully extended length of the PEO block, indicating that the PEO chains confined within the polar layers in the lamellar mesophase were not fully stretched normal to the interface of PB microdomain; alternatively, they adopted a folded conformation while lying on the lamellar plane to alleviate the entropic penalty of the PB blocks while accommodating the formation of lamellar stacks. The secondary force building up the comb structure allowed the order-disorder transition (ODT) from the lamellar phase to a disordered phase in which the comb structure persisted to be accessed easily. Accompanied with this ODT was a concurrent transformation of the PB domain morphology from cylinder to sphere. This demonstrates that, in addition to the structure-within-structure morphology, the supramolecular comb-coil diblock exhibited a transition-driven transition through which the morphology of the larger scale copolymer domain was switched by the ODT of the smaller scale assembly of the comb block.