Synthesis and characterization of novel side chain liquid crystalline polymers by metathesis polymerization

Abstract

A new class of thermotropic side-chain liquid crystalline polymers containing a poly(dipropargylamine) backbone were prepared by metathesis polymerization with transition metal catalysts. It was found that the $\mbox{MoCl_5-EtAlCl_2}$ catalyst systems were very effective for the cyclopolymerization of presently investigated monomers. Resulting polymers exhibited good solubility in common organic solvents such as tetrahydrofuran (THF), chloroform, etc., and could be cast on glass plates to give dark-brown thin films. The structure of the polymers was confirmed by IR, UV-visible, $^1$H- and $^{13}$C-NMR. The number-average molecular weight (Mn) values of the polymers were in the range of $0.65\sim1.8\times{10^4}$, relative to polystyrene standard by GPC. Thermal properties of the monomers and the polymers synthesized were analyzed by differential scanning calorimetry (DSC), cross-polarized optical microscopy, and X-ray diffraction analysis. The electrical conductivity of the polymers was determined by LCR meter. Room-temperature conductivities of the undoped and I$_2$-doped polymers were found to be about $10^{-11}$ and $10^{-3}$S/cm, respectively. Both monomers and polymers displayed enantiotropic liquid crystallinity showing the reversible phase transitions.