The effects of backbone and pendant side-chain structure on the electronic and electrochemical properties of a series of poly[1,4-bis(2-heterocycle)-p-phenylenes] have been studied using a combination of optical spectroscopic, electrochemical, and EPR techniques. The selection of the heterocycle (thiophene or furan) and the nature of the pendant groups, substituted at the 2 and 5 positions of the phenyl ring, were found to impart a strong influence on the types and stability of electrochemically created charge carriers. Substitution with long-chain alkoxy substituents results in a decrease in the monomer and polymer oxidation potentials, narrowing of the electronic bandgap relative to unsubstituted or alkyl-substituted derivatives, and the creation of metallic charge carriers at the highest doping levels. Two oxidation states can be clearly resolved in the cyclic voltammograms of these alkoxy derivatives indicating the formation of stable, polaron species at intermediate doping levels. The synthesis of a new monomer, 1,4-bis(2-thienyl)-2,5-bis[(cyclohexylmethyl)oxy]benzene, and its polymer prepared using both chemically and electrochemically induced oxidative polymerization methods are reported. This monomer displays unique electropolymerization behavior with two oxidative redox processes during electrochemical polymerization. The first redox process (onset ca. +0.65 V vs Ag/Ag+) results in exceedingly slow film growth. Polymer film growth at the second oxidation (onset ca. +0.9 V vs Ag/Ag+) is ca. 25 times more rapid.