Poly(2,5-dialkoxy- p-phenylenebutadiynylene)s—Novel rigid conjugated polymers with liquid crystalline property

Abstract

Novel rigid conjugated poly( p-phenylenebutadiynylene)s having long alkoxy side chains, octyloxy (C8), decyloxy (C10), and dodecyloxy (C12) at 2,5-positions of a phenylene unit, are synthesized by oxidative polycondensation of corresponding 2,5-dialkoxy-1,4-diethynylbenzenes with Hay catalyst. The polymers are soluble in hot solvents such as CHCl 3 and fusible upon heating. UV–Vis spectra of the polymers show an absorption maximum ( λ max) around 420 nm due to the π-conjugation along the main chain. An intense fluorescence exhibiting the λ max around 475 nm is observed in all of the polymers. Cyclic voltammetry of the polymer shows two Li ion-participated redox reactions occurred at the dialkoxyphenylene moiety and in the conjugated polymer chain due to an n-doping process. Electrical conductivity is an order of 10 −8 S cm −1 which increases to an order of 10 −4 S cm −1 upon vapor phase doping by H 2SO 4. Thermochemical investigations by DSC and polarized optical microscopy suggest that the polymers have a nematic liquid crystalline phase. The molecular arrangements in the phase is evaluated by XRD and a molecular dynamics simulation. A nematic phase is shown to arise from a side-by-side accretion of the rigid rodlike main chains. A lamellar structure is suggested in the crystalline phase.