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

Novel rigid conjugated poly(p-phenylenebutadiynylene)s having long alkoxy s ide chains, octyloxy (C8), decyloxy (C10), and dodecyloxy (C12) at 2,5-posi tions of a phenylene unit, are synthesized by oxidative polycondensation of corresponding 2,5-dialkoxy-1,4-diethynylbenzenes with Hay catalyst. The po lymers are soluble in hot solvents such as CHCl3 and fusible upon heating. UV-Vis spectra of the polymers show an absorption maximum (lambda(max)) aro und 420 nm due to the pi-conjugation along the main chain. An intense fluor escence exhibiting the lambda(max) around 475 nm is observed in all of the polymers. Cyclic voltammetry of the polymer shows two Li ion-participated r edox reactions occurred at the dialkoxyphenylene moiety and in the conjugat ed 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) upo n vapor phase doping by H2SO4. Thermochemical investigations by DSC and pol arized optical microscopy suggest that the polymers have a nematic Liquid c rystalline phase. The molecular arrangements in the phase is evaluated by X RD and a molecular dynamics simulation. A nematic phase is shown to arise f rom a side-by-side accretion of the rigid rodlike main chains. A lamellar s tructure is suggested in the crystalline phase. (C) 1999 Elsevier Science S .A. All rights reserved.