SUMMARY:An electroactive material with remarkable solubility, processibility as well as mechanical properties has been developed by complexation (thermal doping) of polyaniline (PANi) emeraldine base with dodecylbenzenesulfonic acid (DBSA) in the solid state. Isothermal treatment of such a mixture was found to promote the complex formation. Optimum conditions of complexation were established with respect to the formation of layered structure, electrical conductivity and solubility. The optimal temperature for the doping process was found to be in a range of 100-120°C while the best ratio of DBSA to PANi was between 3 : 1 and 4 : 1 by weight, a nearly stoichiometric equivalence of aniline repeat units and DBSA molecules. The time of isothermal treatment should be controlled within 30 min. Thermal doping induced orientation to polymer chains in a layered structure, whereby the hydrophobic tails of the surfactants function as spacers between parallel stacks of the main chains. This anisotropy was achieved by the self-assembly during the thermal doping rather than ordinary drawing or stretching of the polymers. A unique liquid crystalline mesophase with a smectic-like optical texture was observed for the soluble portions of some specimens. The excess DBSA in the samples is considered to function as a solvent and to give rise to the liquid crystalline fluidity of the phase. The scanning tunneling microscopy (STM) image 5000 x 5000 A on a submicrometer scale obtained from a P+Ni/DBSA thin film exhibit! a surface morphology with a granular size of 200-300 A. The image of 150 x 150 A on a molecular scale obtained from multilayer PANiIDBSA deposited on a highly oriented pyrolytic graphite (HOPG) surface provides a direct observation of a self-assembled structure and close layer packing of the polymer backbone with dimensions in accord with the results found by X-ray diffraction. Our results indicate that the thermal doping process of polyaniline by DBSA offers new possibilities to obtain optimal structures through a self-assembly.

We have already reported successful carinal reconstruction of the trachea with an observation period of 1 - 2 years. In this study, we evaluate the long-term safety and efficacy of the reconstruction after 5-years of follow-up. The Y-shaped Marlex mesh tube was reinforced with a polypropylene spiral and coated with atelocollagen made from porcine skin. The prosthesis was 60 mm long with an outer diameter of 18 mm. Replacement of the tracheobronchial bifurcation was preformed through a right thoracotomy in a beagle dog. Bronchoscopical examination and sampling of the tracheal epithelium was performed periodically to check the function of cilia. The implanted prothesis was promptly infiltrated by the surrounding connective tissue and completely incorporated by the host trachea and bronchus. Bronchoscopically, sufficient epithelization was confirmed from the upper to the lower site of anastomosis. After 5 years neither stenosis nor dehiscence was observed. In spite of there being mesh-exposure at the luminal surface, the dog had no clinical symptoms until sacrifice for pathological examination. The bent frequency of the cilia was maintained within the normal range, indicating functional recovery of the regenerating airway. Our tracheal prosthesis is promising for clinical repair of the tracheobronchial bifurcation.

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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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