Effects of the polymerization temperature on the structure, morphology and conductivity of polyaniline prepared with ammonium peroxodisulfate

• Polyaniline molecular structure depends on polymerization temperature (Tp).
• Higher Tp leads to decrease of content of non-protonated quinonoid units.
• This was indicated by IR and UV/vis spectra. Raman spectra excluded self-doping.
• Elemental analyses indicated an increase in C/N atom ratio with increasing Tp.
• Temperature dependences of electrical conductivity qualitatively correlated with Tp.

Polyaniline (PANI) samples were prepared by the oxidation of aniline with ammonium peroxodisulfate in a reaction vessel placed in a bath thermostated to particular temperature, Tb, from −20 °C to 40 °C. Temperature–time profiles of reaction mixtures were monitored except for the reaction at −20 °C that proceeded in the solid state. The temperature regime was found to influence the molecular structure, morphology, crystallinity and electrical conductivity of PANI. The increase in Tb results in an increased content of meanwhile unspecified structure defects in the formed PANI chains (the presence of attached self-doping groups is improbable), decreased crystallinity, toughness and compactness of PANI microparticles and increased steepness of the temperature dependence of PANI conductivity. The PANI prepared in the solid-state polymerization at −20 °C shows, besides a rather high crystallinity, the unusually high position of the quinonoid band maximum: 643 nm, which suggests a high regularity of its chains. A correlation between the temperature dependence of PANI conductivity at low temperatures (range from 13 to 318 K) on one hand and the temperature regime of PANI preparation on the other hand, is reported for the first time. The dependences obtained only poorly meet the variable random hopping model.

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