Tunable Conductive Copolymers from Aminophenol and Chloroaniline Show Promising Electrical and Antibacterial Properties

Conducting polymers have long occupied a special place in materials science because they combine the mechanical flexibility of plastics with electrical behaviour that can approach that of semiconductors. Among this family, polyaniline stands out for its ease of synthesis in water, its reversible redox chemistry, and its stability in demanding environments. Yet polyaniline and its substituted relatives carry a persistent weakness: they are poorly soluble in common solvents, which makes them frustratingly hard to process into films, coatings, and devices. A new study published in Results in Chemistry tackles this challenge head-on by chemically copolymerising two functionalised monomers, m-aminophenol and m-chloroaniline, at five different molar ratios, and then mapping in detail how the resulting poly(m-aminophenol-co-m-chloroaniline) derivatives behave spectroscopically, thermally, electrically, and biologically. The work, led by K.A. Ibrahim, demonstrates that simply adjusting the feed ratio of the two monomers provides a powerful dial for tuning the electronic and structural properties of the final material.

The synthetic route is deliberately straightforward. Either m-aminophenol or m-chloroaniline, or both together at ratios ranging from 9:1 down to 1:9, is dissolved in 1 M hydrochloric acid and polymerised at 0–5 °C by the dropwise addition of ammonium persulfate, a strong oxidising agent. After five hours of stirring and an overnight rest, a dark green precipitate of the conducting salt form is recovered, washed, dried, and ground into powder. Yields for the homopolymers and copolymers all exceeded 70 percent, indicating that the oxidative polymerisation procedure is efficient and reproducible. The colour changes that accompany the reaction tell their own story: the initially colourless monomer solution turns blue as oligomeric species form and then deepens to dark green as the emeraldine salt of the conductive polymer accumulates. This autocatalytic behaviour, the study notes, is shaped by the choice of oxidant and the concentrations of both dopant and reactants.

Structural confirmation came primarily from Fourier transform infrared spectroscopy. In the homopolymers, characteristic O–H and N–H stretching peaks appear near 3230 and 3348–3315 cm⁻¹ respectively, while in the copolymers these vibrations merge into a broad band between 3196 and 3244 cm⁻¹, a signature the author attributes to weak hydrogen bonding between the hydroxyl group and nitrogen atoms along the chain. The asymmetric stretching modes of the quinoid and benzenoid rings, found at 1598 and 1495 cm⁻¹ in the homopolymers, shift to 1564 and 1477 cm⁻¹ in the copolymers, confirming the formation of a genuinely conjugated backbone in which both monomer units are incorporated. The C–Cl stretching band, located at 775 cm⁻¹ in homopolychloroaniline, shifts to 779 cm⁻¹ in the copolymers and, crucially, grows in intensity as the chloroaniline fraction of the feed increases, providing direct visual evidence that monomer composition is faithfully transferred into copolymer composition.

Ultraviolet–visible spectroscopy reinforced this picture of a tunable conjugated system. The first absorption band, arising from the π–π* transition of the benzenoid ring, appears at 283 nm for poly(m-aminophenol) and 281 nm for poly(m-chloroaniline), while the copolymers show values that shift with composition, reaching 305 nm at the highest chloroaniline loading. A second broadband near 377 nm corresponds to an n–π* transition, essentially a charge transfer from the benzenoid ring to the quinoid ring, and broad polaron bands in this region indicate significant doping, protonation, and hydrogen bonding within the polymer chain. As the chloroaniline content rises, the absorption maximum red-shifts and the vibronic fine structure sharpens, both hallmarks of an extended π-conjugated system whose electronic structure is being systematically reshaped by the electron-withdrawing chlorine substituent at the meta position.

Perhaps the most striking quantitative result concerns electrical conductivity, measured in solution at 250 ppm in dimethyl sulfoxide. Homopoly(m-aminophenol) conducts at 441.4 μS cm⁻¹, while homopoly(m-chloroaniline) manages only 341 μS cm⁻¹, the latter hampered by the meta-positioned chlorine atom, which produces a non-planar conformation, increases disorder in the backbone, and restricts electron mobility. The copolymers, however, chart a clear upward trajectory as chloroaniline content increases: from 436 μS cm⁻¹ at the 10 percent loading to 989 μS cm⁻¹ at 70 percent, and a maximum of 1277 μS cm⁻¹ at 90 percent. The explanation lies in a productive electronic partnership: electron-rich aminophenol rings sit adjacent to electron-deficient chloroaniline units, generating enhanced electron resonance and charge carriers, while the hydroxyl group promotes conjugation, hydrogen bonding, and electron delocalisation that collectively outweigh the inductive damping effect of chlorine.

Beyond qualitative band assignment, the study exploits FTIR as a genuine quantitative analytical tool. Using the C–N–C absorption near 1280 cm⁻¹ as an internal standard because it appears regardless of composition, and the 779 cm⁻¹ C–Cl band as the composition-sensitive peak, the author applied the Beer–Lambert law with a tangent baseline to calculate absorbance ratios. The ratio of the C–Cl to C–N–C intensities scales linearly with the chloroaniline fraction in the feed, passing through the origin, and the data show high accuracy and reproducibility. This quantitative approach, the paper notes, has broad practical relevance, from monitoring copolymer composition and detecting additives to tracking plastic waste recycling and microplastic pollution, and it demonstrates that infrared spectroscopy can serve as a rapid, solvent-free quality-control method for these conductive materials.

Thermal stability was assessed by thermogravimetric analysis under nitrogen at a heating rate of 10 °C per minute up to 900 °C. All samples showed a characteristic four-stage degradation profile. Initial weight loss between 22 and 100 °C, about 9.3 percent for homopolymers and 6.1 percent for copolymers, reflects the removal of trapped water and physically adsorbed molecules. A second stage between 100 and 200 °C, roughly 16.5 percent, corresponds to the loss of dopant species such as water and hydrochloric acid. The third stage, spanning 200 to 350 °C with a 20–31.5 percent loss, involves the elimination of oligomers and low-molecular-weight fractions, and the final stage from 350 to 550 °C, with a dramatic 76–80 percent decline, represents the chemical breakdown of the backbone itself, leaving a carbon-rich residue of about 20–22 percent. Encouragingly, all homopolymers and copolymers remain thermally stable up to approximately 500 °C, placing them comfortably within the operating window of most electronic and sensing applications.

Scanning electron microscopy revealed how composition sculpts surface morphology. Poly(m-aminophenol) alone displays a rough surface studded with randomly distributed spherical structures on microscopic particles. As the chloroaniline fraction increases, the morphology progressively evolves toward that of poly(m-chloroaniline), and porosity rises in step with composition. This is far from a cosmetic detail: greater porosity means more surface area and more active binding sites, which makes the copolymers attractive candidates for dye adsorption and gas sensing. Related polyaniline derivatives are already proven performers in water purification, with poly-m-chloroaniline removing anionic dyes such as indigo carmine and eosin Y at rates of 98 and 99 percent within 25 minutes, driven by hydrogen bonding, π interactions, and electrostatic attraction between the dye molecules and the amine, imine, and chlorine functional groups on the polymer surface.

The biological findings add an unexpected dimension. Tested by agar diffusion against Gram-negative E. coli and Gram-positive Staphylococcus sp., the polymers showed clear antibacterial activity that tracked with composition. Poly(m-aminophenol) proved most effective against E. coli, while poly(m-chloroaniline) was the weakest, and increasing the chloroaniline content in the copolymers reduced their activity against that organism. The mechanism, as the study and prior literature describe it, rests on the polymers’ ability to form hydrogen bonds with phosphorus- and sulfur-rich components of bacterial cells, including proteins and DNA, and on the positively charged, protonated state of polyaniline-type backbones, which bind to the negatively charged lipopolysaccharide membranes of Gram-negative bacteria. Hydrophobic phenyl segments then disrupt the membrane core, causing leakage of cellular contents, loss of membrane potential, and ultimately cell lysis, while the polymers can also promote the release of hydrogen peroxide and hydroxyl radicals that oxidise bacterial biomolecules.

Taken together, the study shows that chemical oxidative copolymerisation offers a simple yet remarkably effective lever for tailoring conductive polyaniline derivatives. By varying only the monomer feed ratio, the author produced a family of materials whose solubility, conjugation length, conductivity, porosity, and antibacterial potency all shift in predictable, composition-dependent ways. The 1:9 aminophenol-to-chloroaniline copolymer emerged as the best conductor of the series, a result that points toward applications in antistatic materials, chemical sensors, and other electrically active polymer systems where processing ease and tunable conductivity matter. The author cautions that this work focused primarily on synthesis, spectroscopic characterisation, and conductivity, and that future studies should probe how oxidant concentration, acid strength, temperature, and polymerisation time influence molecular weight, morphology, and performance. Even so, the central message is clear: mixing a hydrophilic, electron-donating monomer with a hydrophobic, electron-withdrawing one yields conductive polymers that are more soluble, more processable, and in some cases more biologically active than either parent homopolymer alone.

Subject of Research: Chemical synthesis, spectral characterisation, stability, conductivity, and antibacterial activity of poly(m-aminophenol-co-m-chloroaniline) copolymers

Article Title: Chemical synthesis, quantitative and qualitative spectral characterisation, stability, and biological activity study of some electrically conductive co -polyaniline derivatives

Article References: Ibrahim, K. (2026). Chemical synthesis, quantitative and qualitative spectral characterisation, stability, and biological activity study of some electrically conductive co-polyaniline derivatives. Results in Chemistry, 30, Article 103872. https://doi.org/10.1016/j.rechem.2026.103872

Image Credits: AI Generated

DOI: 10.1016/j.rechem.2026.103872

Keywords: polyaniline, conducting polymers, m-aminophenol, m-chloroaniline, oxidative polymerisation, FTIR spectroscopy, UV-Vis spectroscopy, electrical conductivity, thermal stability, antibacterial activity, copolymerisation, materials science