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Polythiophenes (PTs) constitute a diverse array of promising materials for conducting polymer applications. However, many of the synthetic methods to produce PTs have been optimized only for the prototypical alkyl-substituted example poly(3-hexylthiophene) (P3HT). Improvement of these methods beyond P3HT is key to enabling the widespread application of PTs. In this work, P3HT and two ether-substituted PTs poly(2-dodecyl-2H,3H-thieno[3,4-b][1,4]dioxine) (PEDOT-C12) and poly(3,4-bis(hexyloxy)thiophene) (PBHOT) are synthesized by the FeCl₃-initiated oxidative method under different conditions. Polymerization was carried out according to a common literature procedure (“reverse addition”) and a modified method (“standard addition”), which differ by the solvent system and the order of addition of reagents to the reaction mixture. Gel-permeation chromatography (GPC) was performed to determine the impact of the different methods on the molecular weights (M_w) and degree of polymerization (X_w) of the polymers relative to polystyrene standards. The standard addition method produced ether-substituted PTs with higher M_w and X_w than those produced using the reverse addition method for sterically unhindered monomers. For P3HT, the highest M_w and X_w were obtained using the reverse addition method. The results show the oxidation potential of the monomer and solution has the greatest impact on the yield and X_w obtained and should be carefully considered when optimizing the reaction conditions for different monomers.