Polyanilines template polymerization

Here, electric fields caused the deposition of polyaniline on the patterned template to occur rapidly in one-step and avoided complicated chemistry methods, such as the template polymerization of a conductive polymer and functionalization of the substrate surface. In addition, the use of an external electric field provides a combination of advantages including simplicity, high rates, easy control and prompt response to the ON-OFF cycles of the applied electric field, which may not otherwise be achieved through inherent interactions. It meets the requirements of a low cost, high volume method to pattern conducting polymers for the production of miniaturized complex features needed by industry. 

Similar approach has also been taken by Ferain and Legras [133,137,138] and De Pra et al. [139] to produce nanostructured materials based on the template of the membrane with etched pores. Polycarbonate film was also of use as the base membrane of the template, and micro- and nanopores were formed by precise control of the etching procedure. Their most resent report showed the successful formation of ultrasmall pores and electrodeposited materials of which sizes were as much as 20 nm [139]. Another attractive point of these studies is the deposited materials in the etched pores. Electrochemical polymerization of conjugated polymer materials was demonstrated in these studies, and the nanowires based on polypyrrole or polyaniline were formed with a fairly cylindrical shape reflecting the side wall structure of the etched pores. Figure 10 indicates the shape of the polypyrrole microwires with their dimension changes by the limitation of the thickness of the template. 

The inter-relationship between colloid and polymer chemistries is completed by colloidal polymer particles. The formation of 50-nm-diameter, 100- to 200-nm-long polyaniline fibrils in a poly(acrylic acid)-template-guided polymerization, similar in many ways to those produced from polymerized SUVs (see above), provides a recent example of polymer colloids [449], The use of poly(styenesulfonic acid) as a template yielded globular polyaniline particles which were found to be quite different morphologically from those observed in the regular chemical synthesis of polyaniline [449]. 

FIGURE 5.18 Template-guided polymerization to make water-soluble polyaniline (PanAquas). Aniline monomer is complexed to a polyacid template and then oxidatively polymerized inacontrolled fashion. (After Nguyen, M. T., Kasai, P., Miller, ). L., and Diaz, A. F. 1994. Macromolecules, 27, 3625.)... 

P.-C. Wang, E. C. Venancio, D. M. Sarno, and A. G. MacDiarmid, Simplifying the reaction system for the preparation of polyaniline nanofibers Re-examination of template-free oxidative chemical polymerization of aniline in conventional low-pH acidic aqueous media. React. Funct. Polym., 69, 217-223 (2009). 

There are various methods to synthesize polymer nanostructures, i.e., template synthesis, chiral reactions, self-assembly, interfacial polymerization and electrospinning. Recent developments in conducting polymer nanotubes and nanofibers were summarized by Long et al. Different preparation methods, physical properties, and potential applications of one-dimensional nanostructures of conjugated polyaniline (PANI), pol5 3nrole (PPy) and poly (3, 4-ethylenediox3d hiophene) (PEDOT) were discussed. 

Using functional molecules as structural directors in the chemical polymerization bath can also produce polyaniline nanostructures. Such structural directors include surfactants [16-18], liquid crystals [19], polyelectrolytes (including DNA) [20,21], or complex bulky dopants [22-24]. It is believed that functional molecules can promote the formation of nanostructured soft condensed phase materials (e.g., micelles and emulsions) that can serve as soft templates for aniline polymerization (Figure 7.3). Polyelectrolytes such as polyacrylic acid, polystyrenesulfonic acid, and DNA can bind aniline monomer molecules, which can be polymerized in situ forming polyaniline nanowires along the polyelectrolyte molecules. Compared to templated syntheses, self-assembly routes are more scalable but they rely on the structural director molecules. It is also difficult to make nanostructures with small diameters (e.g., <50 nm). For example, in the dopant induced self-assembly route, very complex dopants with bulky side groups are needed to obtain nanotubes with diameters smaller than 100 nm, such as sulfonated naphthalene derivatives [23-25], fidlerenes [26], or dendrimers [27,28]. 

It has been known since the early stage of conducting polymer research that polyandine fibrils of 100 nm in diameter can naturally form on the surface of an electrode [4,40-45] with a compact microspheriod underlayer. Some recent work demonstrates that pure polyaniline nanofibers can be obtained without the need for any template by controlling the polymerization rate [46—48]. Although this process is not readily scalable from a materials point of view, such work could be very important for making functional devices, since nanofiber-coated electrodes can be used as a platform to fabricate sensors and transistors. Interconnected network-like structures with polyaniline nanoKnkers 10-50 nm wide have also been identified in polymer blends [49-51]. 

Liu, J.M., and S.C. Yang. 1991. Novel colloidal polyaniline fibrils made by template guided chemical polymerization. Chem Commun 21 1529-1531. 

A different method of S3mthesizing polyanUine was reported [77]. It uses an enzyme, horseradish peroxidase, in the presence of hydrogen peroxide to polymerize aniline. To prevent reactions at the ortho positions of the phenyl rings that yield insoluble branched materials, a polyelectrolyte template, like sulfonated polystyrene, was used. The polyelectrolyte aligns the monomers, dopes the polyaniline to the conducting form, and forms an irreversible complex with the polyaniline to keep it water-soluble [77]. The conductivity of the complex increases with increasing polyaniline to sulfonated polystyrene molar ratios. Conductivities of0.005 S/cm are obtained with the pure complex and increase to 0.15 S/cm after additimial doping by exposure to HCl vapor [77]. 

The conventional chemical polymerization of polyaniline only produces nonfibrous or irregular shaped morphologies [237,238], In the past several years, a variety of chemical methods were reported that yield polyaniline nanofibers, such as use of hard templates [239,240], soft templates [241], electrospinning [242], interfacial polymerization [237], and seeding polymerization [238]. Recently, Chiou and Epstein discovered that polyaniline nanofibers can be directly synthesized in dilute chemical polymerization... 

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