Hierarchical Structures of Hydrogen-Bonded Liquid-Crystalline Side-Chain Diblock Copolymers in Nanoparticles

Abstract

Here we show that it is possible to control the overall morphology as well as hierarchical microstructure of lamellae-forming block copolymers within nanoparticles by altering side-chain content and processing temperature. We used cholesteryl hemisuccinate (CholHS) as hydrogen-bonded side chains and poly(styrene)-block-poly(4-vinylpyridine) (PS–P4VP) as backbone to produce submicrometer particles with the aerosol method. With CholHS-to-P4VP repeat unit ratio of 0.25 and 0.50, we obtained onion-like particles with either single CholHS layers sandwiched between P4VP rich lamellae or smectic P4VP(CholHS) layers perpendicular to the polymer domain interfaces. When the fraction of CholHS was increased to 0.75, the onion-like structure broke down due to increased splay deformation energy of the liquid crystalline P4VP(CholHS) domains. The onion-like structure could be re-established, however, when the particles were produced at a higher temperature which made the CholHS molecules partially soluble into the PS phase. Because of the reversible nature of the hydrogen bonds, it was possible to selectively remove the CholHS side chains from the particles.