*2.1. Materials*

As a fiber-forming polymer, polyacrylonitrile (PAN) (Good-Fellow Co., Huntingdon, UK) was used, which contained 99.5 wt.%. polyacrylonitrile and 0.5 wt.%. methyl polyacrylate. Polyaniline was prepared from aniline chloride C6H7N·HCl (Sigma-Aldrich Co., St. Louis, MO, USA) and ammonium persulphate (NH4)2S2O8 (POCH, Gliwice, Poland). Dimethylformamide (DMF) (Chempur, Piekary Sl ˛ ´ askie, Poland) was used as a solvent for the polyacrylonitrile.

### *2.2. Blended Polyaniline (PANI) with Spinning Dope*

Polyaniline (PANI) was obtained by mixing an aqueous solution of 0.5 M aniline hydrochloride (C6H7N·HCl) and 0.6 M ammonium persulfate ((NH4)2S2O8). Ammonia was added to the mixture after 4 h and the resulting precipitate was filtered using a Schott funnel. The obtained precipitate was washed

with methanol, dried at room temperature, and then ground to a fine powder. The polyaniline powder was dissolved in dimethylformamide under the influence of ultrasound. Polyacrylonitrile (PAN) was added to the obtained solution. The weight concentration of polyacrylonitrile in the spinning solution was 13.5%, and polyaniline was approximately 1 wt.% to the weight of polyacrylonitrile. The fibers obtained using this method were marked as PAN/PANI blended.

### *2.3. Synthesis of PANI in Spinning Dope*

The literature data shows that the best convertible polyaniline is obtained in the solution polymerization process [17]. For this reason, in the second method, polyaniline was synthesized in situ during the preparation of the polyacrylonitrile spinning solution in dimethylformamide (DMF). Two solutions in dimethylformamide (containing 1% of dissolved PAN) were prepared with 0.5 M aniline hydrochloride and 0.6 M ammonium persulfate. Both solutions were mixed together for 4 h. The reaction was carried out at a temperature not exceeding 4 ◦C. After 20 h, the obtained reaction mixture was filtered because colorless crystals were precipitated during the reaction (Figure 1).

**Figure 1.** Crystals precipitated during the reaction of polyaniline in dimethylformamide (DMF) after filtration.

Polyacrylonitrile was added to the filtered solution. The solution was heated to 40 ◦C and stirred for 4 h, then cooled for 2 h. In the synthesis of the polyaniline, the same amount of substrates as in the blended method was used. The fibers obtained using this method were marked as PAN/PANI in situ.
