The review describes the relationship between the properties of functionalized polyanilines depending on the nature of the substituents at the aromatic ring.

This work is focused on modifying aniline monomers with various characteristics that allows one to study the effect of the substituent on the respective polymer. A series of new polyaniline (PANI) derivatives based on an ortho-substituted aniline derivative, 2-(1-methylbut-2-en-1-yl)aniline, were synthesized and characterized. The structures and composition of the polymers that we synthesized were confirmed by elemental analysis, proton nuclear magnetic resonance (¹H NMR) spectroscopy, carbon nuclear magnetic resonance (¹³C NMR) spectroscopy, Fourier-transform infrared spectroscopy (FT-IR), and ultraviolet-visible spectroscopy (UV). Characterization by FT-IR and UV-visible spectroscopy techniques indicated that the polymers exist in protonated emeraldine forms. Scanning electron microscope (SEM) results revealed that the surface morphology of the resulting polymers changed from a heterogeneous hierarchical to spherical structure upon changing the substituent in the aniline monomers. The polymers are soluble in common organic solvents, so they can be used to make films. The electrical properties of the polymers were studied and their high sensitivity to moisture and ammonia was demonstrated. The results of the studies showed the prospects of using thin polymer films in the design of chemical sensors. The impact of the substituent on the polymer characteristics is rationalized in terms of steric and electronic effects.

A new soluble polymer on 2-[(2E)-1-methyl-2-buten-1-yl]aniline and its copolymers with aniline basis have been synthesized in various molar ratios. For all samples, the electrical conductivity, morphology, solubility, electrochemical properties, as well as spectral and molecular mass characteristics have been studied, and a comparative analysis with polyaniline has been carried out. The substituent introduced into the aniline aromatic ring significantly improves the solubility in typical organic solvents of a high molecular weight product. The morphology of the test compounds depends on the co-monomer ratio. As the content of the substituted aniline in the initial mixture increases, the morphology of the polymer changes from the inherent polyaniline fibrous microstructure to the globular one with irregular substituted polyaniline shapes and sizes. Electrochemical study of the samples revealed that the higher the oxidation potential, the wider the band gap (ranging from 2.00 to 2.15). The electrical conductivity decreases in proportion to the increase in the substituted aniline concentration of the initial co-monomer mixture and amounts to 12.5–35.7 × 10⁶ nSm.

Humidity control and monitoring are of great interest for a wide range of applications, including moisture-sensitive products, storage of medicines, and environmental monitoring for keeping valuable antiques or paintings. In this regard, the research priority is the development of a sensitive material for humidity sensors that ensure high performance and sensitivity, and can operate at room temperature as well. Electrically conductive polymers are the most promising candidates among the materials used for humidity sensors. This study is the first report that includes the experimental data on the use of a wide range of new substituted polyaniline (PANI) derivatives as a sensitive material in sensors. The influence of various structural factors such as environmental conditions, the position and number of substituents, and the nature of the doping agent on the sensitivity of polymer materials to changes in humidity was studied. It was found that the use of PANI derivatives as a sensitive material in resistive sensors resulted in a high electrical conductivity response to changes in humidity (% RH). N-substituted and Cl-containing ortho-substituted PANIs showed the smallest response compared to bulky alkyl and cyclo-alkyl substituted polymers, which demonstrated the highest response. In addition, the PANI derivative-based sensors exhibited humidity sensing properties in the broad humidity range of 20–90%. The presented results demonstrate that the modification of PANI by introducing a substituent into the aromatic ring not only improves the solubility but also increases the sensitivity of the material to environmental humidity due to the formation of a porous structure with a large surface area.