Effects of the polymerization temperature on the

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Aug 30, 2013 - Polyaniline (PANI) samples were prepared by the oxidation of aniline with ammonium per- oxodisulfate in a reaction vessel placed in a bath ...

European Polymer Journal 49 (2013) 3904–3911

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European Polymer Journal journal homepage: www.elsevier.com/locate/europolj

Effects of the polymerization temperature on the structure, morphology and conductivity of polyaniline prepared with ammonium peroxodisulfate Michal Bláha a,⇑, Martin Varga b, Jan Prokeš b, Alexander Zhigunov a, Jirˇí Vohlídal c a

Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Heyrovského sq. 2, CZ-162 06 Prague 6, Czech Republic Charles University in Prague, Faculty of Mathematics and Physics, V Holešovicˇkách 2, CZ-180 00 Prague 8, Czech Republic c Charles University in Prague, Faculty of Science, Department of Physical and Macromolecular Chemistry, Hlavova 2030, CZ-128 40 Prague, Czech Republic b

a r t i c l e

i n f o

Article history: Received 1 March 2013 Received in revised form 8 August 2013 Accepted 13 August 2013 Available online 30 August 2013 Keywords: Polyaniline Conductivity Morphology Electronic spectra Infrared spectra

a b s t r a c t 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. Ó 2013 Elsevier Ltd. All rights reserved.

1. Introduction Polyaniline (PANI) is one of the most intensively studied conducting polymers with a wide application potential as a functional polymer [1]. PANI is most often prepared by oxidation of aniline by ammonium peroxodisulfate in acidic aqueous environment. Since this polymerization is a strongly exothermic process [2,3], the temperature of a reaction mixture is not easy to control and its increase can potentially influence the structure and properties of formed PANI. Partial knowledge on the effect of polymerization temperature on the molecular weight [4–11] and conductivity [4,7,8,10–12] of PANI was reported. These ⇑ Corresponding author. Tel.: +420 296809288. E-mail addresses: [email protected] (M. Bláha), [email protected] (J. Vohlídal). 0014-3057/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.eurpolymj.2013.08.018

effects were most in detailed examined by Stejskal and co-workers [10], who reported (i) increase in the molecular weight and crystallinity of PANIs prepared at temperatures below 0 °C, (ii) change from granular to macroporous morphology for PANIs prepared in the solid (frozen) state polymerization and (iii) little dependence of the conductivity on the reaction temperature and molar mass of PANI. The effect of the polymerization temperature regime on the molecule structure, morphology and spectroscopic properties of PANI has yet not been properly reported. Therefore, we decided to examine these questions more in detailed and in addition, to use the PANIs prepared under the controlled temperature regime to examine the temperature dependence of the electrical conductivity of PANI at low temperatures (

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