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Condensation reactions of mono- and didodecyl-substituted-2,5-diformylthiophene with hydrazine, p-diaminobenzene, 2,7-diaminofluorene, and 1,5-diaminonaphatalene give the corresponding polyazines (PAZs) and polyazomethines (PAMs), which have been characterized by thermal, structural, and optical analyses. The former polymers begin to decompose at 300 °C, while the latter polymers are stable up to 360 °C. All disubstituted polymers and the regioregular monosubstituted polyazines show nematic character. Disubstituted polymers display a larger conjugation with respect to monosubstituted ones. This effect has been attributed to a different conformation of thiophenic rings versus imino-linkages assumed by the polymeric backbone in the two classes of polyazines. Particular attention has been devoted to study the reactivity of mono- and disubstituted dialdehydes toward condensation with nucleophiles displaying different steric hindrance or power. Specifically the study of the reaction onset allowed us to determine the conditions to obtain regioregular monosubstituted polymers even with hydrazine, which is the less hindered and the more powerful nucleophile used.