Aniline oligomers

Figure 29 Some of the molecular structures used to interpret the EPR spectra of poly(aniline) oligomers. The molecules are labelled 1 and 4 in the same fashion as Ref. [149].

The first reported optically active PAn s were the PAn/(+)-HCSA and PAn/(-)-HCSA salts (HCSA = 10-camphorsulfonic acid), prepared in our laboratories by the electropolymerization of aniline in the presence of either (+)- or (-)-HCSA.68 69 The optically active dopant anions are believed to induce a preferred one-handed helical arrangement in the PAn chains in these emeraldine salts 4, giving rise to intense CD bands in the visible region. Recent studies by Li and Wang70 have shown that PAn/(+)-HCSA films of exceptionally high optical activity can be electrochemically deposited by polymerizing the aniline monomer in the presence of small amounts of aniline oligomers. 

The formation of PANl-NFs during electrochemical polymerization has been attributed to the combined effect of an electrophilic substitution reaction mainly taking place at the para position of aniline or its oligomers, and aniline oligomers with 1-D structures [290]. It was discovered that the PANl film formed on the electrode exhibited a lamellar structure. Firstly, a thin compact 2-D PANl layer was formed during the initial stage of electrodeposition. Subsequently, microgranular, nanorod-shaped, and nanofibrillar PANl layers were formed from bottom to top, respectively. 

Another study by Hong et al. also reports the preparation of conducting PANI/nylon-6 composites with high electrical conductivity and superior mechanical properties, such as flexibility and lightness [24]. PANI was chemically polymerized on the surface of the nylon-6 electrospun nanofiber webs. The electrical conductivity measurements showed that the conductivity of the PANI/nylon-6 composite electrospun fiber webs was superior to that of PANI/nylon-6 plain-weave fabrics because of the high surface area/volume ratios. The volume conductivities of the PANI/nylon-6 composite electrospun fiber webs increased from 0.5 to 1.5 S cm as the di sion time increased from 10 min to 4h because of the even distribution of PANI in the electrospun fiber webs. However, the surface conductivities of the PANI/nylon-6 composite electrospun fiber webs somewhat decreased from 0.22 to 0.14 S cm as the di sion time increased, probably because PANI was contaminated with aniline monomers, aniline oligomers, and some alkyl chains, which served as electrical resistants. 

When an enantiomer of CSA is used in the polymerization, such as R-CSA, it is possible to create chiral polyaniline nanofibers. Figure 7.20 shows the circular dichroism (CD) spectrum of a water dispersion of as-prepared R-CSA doped polyaniline nanofibers. The positive peak at 450 nm is characteristic of chiral polyaniline [66-70], and is consistent with water s effect on the direction of the CD signals previously observed [71]. The peak at 290 nm is due to excess R-CSA in the dispersion. Recently, Wang et al. discovered that highly chiral polyaniline nanofibers can be produced by incremental addition of the oxidant, ammonium peroxydisulfate, into aniline solution with aniline oligomers and concentrated chiral dopants (>5 M R- or S-CSA) [72]. Chiral polyaniline nanofibers are very interesting for chiral recognition studies [68]. 

PANI nanofiber has been also prepared using ohgomer-assisted synthesis [289]. In this method, the polymerization has been carried out in concentrated CSA solution, and aniline oligomers are used to accelerate the polymerization reaction. The resultant PANI nanofiber showed the diameter in ranges from 20 to 40 nm with several micrometer lengths. 

A comparative ab initio and DFT study of neutral aniline oligomers ... 

The choice of acids has also other effects on the nanostructure for example, the use of tetrachloroaurate as an efficient oxidant of aniline in the presence of a chiral inducing agent, i.e. (15)-(+)-10-camphorsulfonic acid ((5)-(+)-CSA) or its enantiomer (A)-(-)-CSA, allows the formation of optically active PANI nanorods, together with the further self-assemblies into monodispersed hierarchical Au (0) microspheres [103]. Recently, aniline oligomers have also received attention, because they can be envisaged as the building blocks of block architectures... 

Con arison to PANI and the aniline oligomers revealed that these electroactive polyimides owed relatively high oxidation potentials. The oxidation resistance of TANI-imide can be attributed to the electron withdrawing terminal imide groups. 

Electroactive Aniline Oligomers of Well-Defined Structures and Their Polymeric Derivatives... 

There have been a number of methods reported for the preparations of aniline oligomers in the literature. Most of them involved multi-step synthetic reactions or unstable reagents. Since later 1980s, Wei and coworkers have been interested in the development of fundamental understanding of the polymerization mechanism and, therefore, better methodologies for the synthesis of electroactive polymers including... 

Fig. 2. Plot of Log(conductivity) vs. number of anilino unit in the aniline oligomers, doped with 1 M HCl. Unit of...

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