Synthesis and characterization of new thermotropic side-chain liquid crystal polymers containing 1,6-heptadiyne backbone

Poly(l,6-heptadiyne) derivatives with side-group liquid crystalline mesogens are prepared by ring-forming metathesis polymerization with transition metal catalysts. MoCl₅-based catalyst systems are more effective for the polymerization of 1,6-heptadiyne monomers with various mesogenic groups than are WCl₆-based catalyst systems. The resulting polymers exhibit good solubility in common organic solvents such as chloroform and THF, and they can be easily spin-coated on ITO glass. The weight-average molecular weights of the polymers are in the 3.5 to 26 x 10⁴ range relative to polystyrene standards by GPC. The ¹H-, ¹³C-NMR, and IR spectra of the resulting polymers indicate that side-chain liquid crystal polymers with a 1,6-heptadiyne backbone possess a polyene structure, presumably with cyclic recurring units in the polymer backbone. Thermal behaviors, morphology, and electrical conductivities are investigated by using differential scanning calorimetry, cross-polarized optical microscopy, and an LCR meter. M-1 and P-1 displayed enantiotropic liquid crystallinity showing reversible phase transition. M-2 and P-2 displayed no mesophase. The electrical conductivities of the film-type polymers are in the 10 ^–4 to 10 ^–2 S/cm range.