Incorporation of flexible alkyl chains into polyaniline was accomplished through an N-alkylation method with the leucoemeraldine form in order to maximize the degree of alkylation. The number of carbons varied from butyl to octadecyl, and with dodecylated samples, the degree of substitution was also controlled. The solubility in common organic solvents improved remarkably with the alkylation. The polymers displayed interesting solvatochromism and thermochromism, which result from the conformational changes induced by the interactions between the polymer and the solvent molecules and from the cooperation of disordering of the side chains and twisting in the main chain upon heating. In the solid state, the polymers form a layered structure in which the distance between the backbones depends on the length of alkyl side chain as recorded by the d spacing in WAXD patterns. DSC studies revealed that glass and melting transitions decreased systematically by increasing the length of substituents. With increasing side-chain length, the degree of interdigitation increases and the side chains begin to crystallize in a hexagonal packing array as determined by DSC, WAXD, and FT-IR data. The critical length n for side-chain crystallization is a minimum of 14 carbons, which is much larger than in the case of polyacrylates and polythiophenes, indicating the more rodlike character of polyaniline backbones. In addition, with polymers of n greater than or equal to 16, a mesophase transition after melting of the side-chain crystallites can be detected by optical microscopy and DSC.