Tuning Structures of Mesogen-Jacketed Liquid Crystalline Polymers and Their Rod-Coil Diblock Copolymers by Varying Chain Rigidity

Two mesogen-jacketed liquid crystalline (LC) polymers with different rigid side-chain cores, poly[2,5-bis(tert-butoxylcarbonyl)styrene] (PM1) and poly[2,5-bis(4-tert-butoxylcarbonyl phenyl)styrene] (PM3), as well as their corresponding block copolymers (BCPs), poly(dimethylsiloxane)-b-PM1 (PDMS-b-PM1) and PDMS-b-PM3, are synthesized and characterized. The LC phase structures of the homopolymers and the microphase-separated structures of the BCPs can be controlled by changing the rigidity of the polymer chains with the different rigid side-chain cores used. The LC phase structure of PM1 homopolymer is dependent on its molecular weight (MW). On the other hand, PM3 is always amorphous below thermal decomposition temperature regardless of its MW, owing to much higher rigidity of PM3 compared with that of PM1. Although both BCPs can self-assemble into lamellae (LAM) and hexagonally packed cylinders (HEX) with varying compositions, PDMS-b-PM3 can form the HEX structure at a smaller weight fraction of the PM3 block because PDMS-b-PM3 possesses a larger geometric asymmetric factor compared with PDMS-b-PM1. For PDMS-b-PM1 with a large enough MW, it can form hierarchically ordered nanostructures, including the LAM or HEX nanostructure of the BCP and the columnar nematic phase of the PM1 block.