Preparation of Water-Soluble Homo and Copolymers of Bithiophene with 3,4-Ethylene Dioxythiophene and 3-Dodecylthiophene in Presence of Polystyrene Sulfonic Acid: Structure, Morphology, Thermal Stability

Conductive polymers based on water-soluble polythiophenes were prepared. In this respect, alkylation reaction was carried out to synthesize the monomer 3-dodecylthiophene using 3-bromothiophene, bromododecane and magnesium. The monomer 2,2′-bithiophene was also prepared from 2-bromothiophene. Then, poly(2,2′-bithiophene), poly(3,4-ethylenedioxythiophene) and poly(3-dodecylthiophene) homopolymers were prepared at room temperature by successive chemical oxidation in the presence of polystyrene sulfonic acid and ammonium persulfate and water, as dopant, oxidant and solvent, respectively, under vigorous stirring. Under similar conditions, 2,2′-bithiophene copolymers with 3-dodecylthiophene and 3,4-ethylenedioxythiophene, copolymers with 3-dodecylthiophene were prepared at different molar ratios. To purify and dry the prepared polymers, dialysis tubs and freezing dry processes were applied. Structure of homo and copolymers were investigated by Fourier transform infrared (FTIR). Conjugated and planar structures of polymers were studied by Ultravoilet (UV-vis) spectroscopy. The electrical conductivity of synthesized polymers was measured by four probe technique. The morphology and thermal stability of the products were studied using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). Finally, solubility of homo and copolymers were tested in some organic solvents and water. Electro- activity of the prepared polymers was studied by cyclic voltammetry (CV) on the glassy carbon (GC) in LiClO₄/CH₃CN electrolyte solution and their electro-activity was confirmed. Electro-conductivity and electro-activity of homo and co polymers were low due to
presence of polystyrene sulfonic acid which reduced the immobility of the polymers.