Synthesis and properties of liquid crystalline conjugated polymers

We have synthesized novel side-chain liquid crystalline (LC) conducting polymers by introducing LC groups into acetylene monomers and polymerizing them with Ziegler-Natta [Fe(acac)(3)-AlEt3], metathesis [MoCl5-Ph4Sn], and rhodium-based {[Rh(NBD)Cl](2)NEt3} catalysts. All polymers prepared exhibited solubility in organic solvents and smectic liquid crystallinity characterized by fan-shaped texture in polarizing optical microscopy. Phase transitions and the corresponding enthalpy changes were evaluated by means of differential scanning calorimetry (DSC). High order structures of the LC polyacetylene derivatives were investigated by means of X-ray diffraction (XRD) analysis. XRD measurements elucidated that all of the polymers showed layered structures in the LC states to give smectic A phases, which is in agreement with the results from the polarizing optical microscopy. It is found that the LC side chains are alternatively located on both sides of the polyene chain, giving rise to a stereoregular sequence such as a head-head and tail-tail linkage. Macroscopic alignments of the polymers were performed in the LC phase by shear-stress or magnetic force field of 0.7 similar to 1.0 Tesla, which resulted in an enhancement by two orders in electrical conductivity of iodine-doped cast films. Magnetically forced alignments and orientational behavior of the polymers as well as the monomers were investigated through fused-state C-13 NMR measurements with proton dipolar decoupling. Analysis of chemical shift tensors was carried out to evaluate the order parameter and shielding anisotropy in the LC phase. As a result, it is demonstrated that the LC conjugated polymers are uniaxially aligned as a result of the magnetically forced alignment of the LC side chain, forming a mono domain structure.