Macroscopic Alignment of the Self-assembled Polymer Helix by a Magnetic Field

2 Macroscopic Alignment of the Self-assembled Polymer Helix by a Magnetic Field 

In the previous section, we reported PMP derivatives bearing chiral side chains having a helicene-like helical structure through intrachain 7r-electron overlap interactions, which lead to a self-assembled whisker morphology due to interchain van der Waals interactions. However, each whisker of the PMP derivative is still randomly oriented, even if it has a self-assembled structure. It is therefore desirable to align the PMP derivative to construct a higher-ordered hierarchical structure and also to evolve an anisotropic nature in its potentially profound op-toelectrical properties. 

we synthesized liquid crystalline PMP derivatives by introducing phen-ylcyclohexyl (PCH) or cyanobiphenyl (CB) LC groups into the side chains and macroscopically aligned the polymers in LC phases using a magnetic field of 12 T [13]. Poly-2 (Mn = 8,400) has PCH side chains linked with flexible dodecam-ethylene chains via ester moieties. Poly-3 (M — 8,500), on the other hand, has a CB LC moiety in its side chain (Fig. 11.6). 

The macroscopic alignment of the polymers was carried out under a magnetic field. The polymer sample supported on an aluminum plate was inserted into a mantle heater and placed in the middle of a superconducting magnet. The polymer was first heated to an isotropic temperature and then cooled to its LC temperature, at which a magnetic field of 12 T was applied for 30 min. Then, the polymer was slowly cooled to room temperature under a magnetic field. 

POM characterization revealed that Poly-2 has a batonnet-like texture from 125 to 94 °C and a fan-shaped texture from 94 to 80 °C during the cooling process. On the other hand, Poly-3 has a sandy texture from 142 to 112 °C and a batonnet-like texture from 112 to 93 °C during the cooling process. XRD measurements revealed that Poly-2 has a discotic nematic (No) phase at higher LC temperatures and a discotic lamellar (Dl) phase at lower LC temperatures. Poly-3 showed a Nq phase and a hexagonal columnar (CoL) phase at higher and lower LC temperatures, respectively. The phase transition temperatures of Poly-2 and Poly-3 are summarized in Table 11.2. 

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