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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 > 16, a mesophase transition after melting of the side-chain crystallites can be detected by optical microscopy and DSC.* To whom the correspondence should be sent.

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ABSTRACT:The influence of various organic dopants on the structure of N-alkylated polyanilines substituted with alkyl side chains of different lengths and at different degrees of alkylation has been studied by FT-IR, UV-Visible spectroscopies, and X-ray diffraction. The results show that the protonation as seen for polyaniline emeraldine base can be achieved successfully through the doping method in our experiments. The conductivities of the doped polymers decrease with increasing the length of side chains and the degree of alkylation. The polyanilines doped with methanesulfonic acid (MSA), toluenesulfonic acid (TSA), and dodecylbenzenesulfonic acid (DBSA) induce a co-operative effect with the alkyl side chains on the formation of layer order. Small dopants distort the layered structure and prevent the crystallization of the side chains. The interaction of the alkyl side chains and alkyl group in DBSA assist in the development of the layered structure.KEY WORDS Polyaniline I Doping I Layer Formation I Polyaniline has been recognized as an interesting conducting polymer though its intractability has limited the comprehensive understanding of its structure as well as the potential applications. Recently, it has been found that this barrier can be overcome by the incorporation of flexible side chains to the stiff backbones leading to highly soluble polyanilines. The resulting polyanilines are fusible or soft below the temperatures where crosslinking or thermal decomposition prevails. 1 · 2 Furthermore, these alkyl substituents induce the formation of a layered structure, side chain crystallinity, mesophase, and thermochromic behavior. 3 As the side chains in the layered structure "melt" or disorder, the sheets consisting of a parallel array of main chains can quickly respond to external shear, which renders this layered structure significant for melt or solution processing. Although a relatively large volume of alkyl side chain segments has been added to polyaniline, the substituted main chains still retain the basic conjugated structure and basic optical properties.The control of the properties of the conducting polymers by the process of doping is currently under intense scrutiny. 4 · 5 Doping not only initiates an increase in conductivity of the initially neutral conjugated polymer, but also leads to remarkable changes in proccessability, morphology, and mechanical properties. 6 -8 Recently, an important innovation by the use of surfactants with polyaniline has attracted great attention in the academic and industrial research community. 9 · 10 Since these dopants, such as dodecylbenzene sulfonic acid (DBSA) and camphorsulfonic acid (CSA), can perform as plasticizers, the doping of intractable polyaniline creates soluble and processable forms of the parent polymers. The complex of polyaniline and DBSA has been found to form a well-defined layered, smectic-like structure in which the alkyl chains function as spacers between parallel stacks of the polymer backbones. 11 From the experimental and theoretical analyses...

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