Synthesis and properties of liquid crystalline conjugated polymers

We have synthesized novel side-chain liquid crystalline (LC) conducting pol ymers by introducing LC groups into acetylene monomers and polymerizing the m with Ziegler-Natta [Fe(acac)(3)-AlEt3], metathesis [MoCl5-Ph4Sn], and rho dium-based {[Rh(NBD)Cl](2)NEt3} catalysts. All polymers prepared exhibited solubility in organic solvents and smectic liquid crystallinity characteriz ed by fan-shaped texture in polarizing optical microscopy. Phase transition s and the corresponding enthalpy changes were evaluated by means of differe ntial scanning calorimetry (DSC). High order structures of the LC polyacety lene derivatives were investigated by means of X-ray diffraction (XRD) anal ysis. XRD measurements elucidated that all of the polymers showed layered s tructures 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 t he LC side chains are alternatively located on both sides of the polyene ch ain, giving rise to a stereoregular sequence such as a head-head and tail-t ail linkage. Macroscopic alignments of the polymers were performed in the L C 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 orientation al behavior of the polymers as well as the monomers were investigated throu gh fused-state C-13 NMR measurements with proton dipolar decoupling. Analys is of chemical shift tensors was carried out to evaluate the order paramete r 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 s tructure.