Soln.-cast films of four different poly(2,5-dialkoxy-p-phenyleneethynylene) mols. with varying backbone chain lengths and varying alkoxy substituent chain lengths and 1,4-diethynyl-2,5-dihexadecyloxybenzene-9,10-dibromoanthracene alternating copolymer (I) have been characterized electrochem. and by x-ray diffraction and DSC. The polymers have varying degrees of order and crystallinity based on long-range lamellar structure. Cyclic voltammetry in liq. SO2/electrolyte shows that the onset of oxidn. for poly(2,5-dialkoxy-p-phenyleneethynylene) occurs at ∼1.05 V vs SCE with the more cryst. polymers having slower electrochem. response than the less cryst. ones. In situ characterization of the potential dependence of cond. in the same medium shows that the max. conductivities of poly(2,5-dialkoxy-p-phenyleneethynylene) range from ∼0.2 to ∼5 $Ømega$-1 cm-1, suggesting that higher cond. is assocd. with lower long-range order in the polymer films but showing little dependence on av. polymer chain length. Poly(2,5-dialkoxy-p-phenyleneethynylene) all have max. cond. at ∼1.6 V vs SCE and finite potential windows of high cond. ∼0.55 V wide, indicating that the potential of max. cond. and the width of the window of high cond. are detd. by mol. rather than bulk properties. For I, the onset of oxidn. occurs at ∼0.8 V vs SCE, the potential of max. cond. is ∼1.5 V vs SCE, and the width of the potential window of high cond. is ∼0.85 V. [on SciFinder(R)]