Chemical Polymerization of Anilines

Electropolymerization in acidic media affords free-standing films that are believed to contain varying degrees of cross-linking [267,292,304]. The miscibility of aniline with water allows for a variety of aqueous oxidants, such as ammonium peroxydisulfate, to be used [305]. Chemical polymerization of aniline can also be performed in chloroform through the use of tetrabutyl ammonium periodate [306]. Accordingly, a number of alkyl [301] and alkoxy-substituted [307] aniline derivatives have been chemically polymerized. Unfortunately, functionalization of the aniline nucleus often leads to a decrease in performance in the resulting polymers [308,309]. 

This section discusses the reactivities and biosensor applications of functionalized electrosynthetic polyanilines prepared by (i) electropolymerization and (ii) chemical polymerization of aniline on the surfaces of Au, glassy carbon or Pt disk electrodes. Four such polyaniline or substituted composite polyaniline films developed by our research group are (a) nanofibrillar polyaniline-polyvinyl sulfonate (PANI-PVS), (b) poly(2,5-... 

Chemical polymerizations of aniline with (NH4)2S208 were initially performed at room temperature. However, later studies showed that the PAn obtained was of relatively low molecular weight and contained significant defect sites such as undesirable branching due to ortho-coupling.5960 Subsequently, the most widely employed temperature for chemical polymerization of aniline monomers has been ca. 1-5°C, as described by MacDiarmid and coworkers,61 providing a PAn whose emeraldine base (EB) forms have molecular weights (Mw) of 30,000-60,000 g mol-1. 

The chemical polymerization of aniline at the interface between two immiscible solvents provides an attractive alternative route to PAn s. Such interfacial polymerization was first demonstrated in 1994 by Michaelson and McEvoy,82 who produced a freestanding PAn film at the interface between a solution of aniline/sodium dodecylsulfate in carbon tetrachloride and an aqueous oxidant solution containing ammonium persulfate/HCl. The analogous interfacial polymerization of a range of /V-alkylanilincs and o-alkylanilines using hexane and water phases for chemical oxidation with ammonium persulfate has also been briefly described.83... 

Redoping an EB sample prepared by chemical polymerization of aniline in HC1 solution giving ES-C1 and subsequent deprotonation using ammonium hydroxide... 

An elaboration of this technique, incorporating the concept of template-guided synthesis, is the use of nanoporous matrices such as zeolites and polycarbonates as a template within whole pores to perform the chemical polymerization of aniline monomers. For example, Wu and Bein254 have prepared nanofilaments of conducting PAn in the 3-nm-wide channels (pores) of the aluminosilicate host, MCM-41, through initial adsorption of aniline vapor into the dehydrated host followed by oxidation with (NH)2S208. 

Figure 2.5 Schematic diagram illustrating the formation of PANI agglomerates during conventional chemical synthesis [the oxidant (open circles), aniline (solidcircles)]. (Reprinted with permission from Angewandte Chemie Int. Ed., Nanofiber formation in the chemical polymerization of aniline A mechanistic study by J. Huang and R. B. Kaner, 43, 5817-5821. Copyright (2004) Wiley-VCH)...

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). 

The use of self-assembled monolayer formation has been adapted to the deposition of conducting-polymer nanofilms by the chemical polymerization of aniline at an amino-silane surface that acts as the seed layer for polymerization, which led to a more ordered nanofibrous growth than would be seen using bulk chemical polymerization [39]. This was shown to be capable of detection of 0.5 ppm ammonia vapor, with a... 

Figure 14.7 TEM ofPANI hollow spheres produced by chemical polymerization of aniline on polystyrene particles and removal with tetrahydrofuran, and decorated with gold nanoparticles. (Reprinted with permission from Langmuir, Polyaniline / Au composite hollow spheres Synthesis, characterisation, and application to the detection of dopamine by X. M. Feng, C.J. Mao, C. Yang et al., 22, 9, 4384-4389. Copyright (2006) American Chemical Society)...

Chemical Synthesis The aniline solution in 1 M HCl was oxidized by ammonium persulfate solution at 4 °C. The molar ratio of the oxidant to monomer was 0.25 to 1. Other details of the chemical polymerization of aniline have been described (17). 

Huang, J.X., and R.B. Kaner. 2004. Nanofiber formation in the chemical polymerization of aniline A mechanistic study. Angew Chem Int Ed 43 (43) 5817-5821. 

Chemical polymerization of aniline has been carried out in an acidic solution [91-101]. This acidic condition provides the solubilization of the monomers as well as the formation of emeraldine salt as a conducting PANI. Scheme 3 depicts a chemical polymerization mechanism of aniline in acidic... 

FeSj/polyaniline (PANI) composite as cathode material for LIB was synthesized via in-situ chemical polymerization of aniline in the presence of fine FeS particles in aqueous suspension. The FeS /PANI composite exhibited the capacity of 767.5 mAh/g at a current density of 100 mA/g with weaker polarization and improved reversible capacity, compared with the FeSj particle. The improvement of the electrochemical properties was due to the enhanced electrical conduction and the buffer connection of amorphous polymer between the particles of the composite [56]. 

Tzou, K., and R.V. Gregory. 1992. Kinetic study of the chemical polymerization of aniline in aqueous solutions. Synth Met 47 267. 

A variety of oxidants have been used to elfect chemical polymerization of aniline under acidic conditions, pH 1-3. It is very strange to note that there is no relationship between the oxidation potential of the reagent and the polymer yield however, our experience in polyaniline synthesis suggests that a simple oxidizing agent like ammonium peroxydisulphate yields a polymer of better quality than oxidizing agents contain-... 

PANI and its derivatives can be synthesized by the electrochemical polymerization or chemical polymerization of aniline although some other approaches have also been reported such as solid-state polymerization [313], electroless polymerization [314], plasma polymerization [315], and emulsion polymerization [307], Various oxidants were used for oxidation of aniline monomer, such as ammonium peroxy-disulfate, sodium peroxydisulfate, potassium bichromate, and hydrogen peroxide. 

Spherical ultra-fine polymer particles (10-35 nm) were prepared by chemical polymerization of aniline in an inverse water-in-oil microemukion [42]. This micro emulsion method provided a denser, more uniform and compact film of higher condensation than that produced in an aqueous medium [16]. 

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