Hierarchical Structures in Lamellar Hydrogen Bonded LC Side Chain Diblock Copolymers

We show that in a hydrogen bonded LC side chain diblock copolymer with lamellar morphology on the block copolymer level, two distinct packing mechanisms of the side chain blocks are possible depending on the amount of hydrogen bonded side chains. We mixed a hydrogen bonding mesogen, cholesteryl hemisuccinate (CholHS), with poly(1,2-butadiene)-block-poly(2-vinylpyridine) (PBd-P2VP) and poly(styrene)-block-poly(4-vinylpyridine) (PS-P4VP), in which the poly(vinylpyridine) act as host blocks, and we varied the CholHS to pyridine repeat unit ratio (x). With all x, a lamellar morphology on the block copolymer level was achieved. However, at low binding of CholHS to the host block, the CholHS side chains microphase separated into a single layer inside the poly(pyridine) lamellae resulting in a novel microphase separated structure. This includes, for example, the PS-P4VP sample with x = 0.25 and all the PBd-P2VP based samples since hydrogen bonding of ChoIHS to P2VP was sterically limited as revealed by infrared spectroscopy. No such limits were present in the rest of the PS-P4VP samples which showed a gradual shift from the single ChoIHS lamella morphology to exclusively liquid crystalline smectic layers oriented perpendicular to the block domain interfaces.