Synthesis and mesomorphic properties of side-chain polynorbornenes containing mono-, di- and tri-calamitic mesogenic pendant groups

Abstract

Side-chain polynorbornenes (PNBs) containing alkoxy biphenyl mesogenic side groups with a controlled number and substituted position within each repeating unit were synthesized and characterized. Various thermotropic mesophases including the smectic A (SmA) phase, the modulated smectic phase with a centered rectangular columnar lattice (Φ_r-c), and the hexagonal columnar (Φ_h) phase have been verified in this system. The influence of the number and position of alkoxy biphenyl groups on the self-assembly behavior of PNBs has been systematically studied. When increasing the number of substituted mesogenic groups, the mesophase of PNBs changes from SmA of PNB-4-CmBA to Φ_r-c of PNB-3,4-CmBA and Φ_h of PNB-3,4,5-CmBA (m = 12, 16). The self-organized structure is determined by the curvature of the interface between the aliphatic and aromatic segregated regions. With increases in the mesogenic group numbers, the interface becomes increasingly curved giving rise to structure alteration. When changing the substituent position from PNB-3,4-CmBA to PNB-3,5-CmBA (m = 12, 16), the phase structure changes from Φ_r-c to the amorphous phase because of the more flexible side chain. The calamitic mesogen shown here is a powerful side-chain building block to construct side-chain polymers with complex supramolecular self-assembled structures.