In the last few decades, conductive polymers have come into the focus of research interest due to their specific characteristics. Excellent stability and biocompatibility, excellent electrical and optical properties, corrosion resistance and low weight, workability and ease of synthesis have combined the positive aspects of metals and conventional polymers. Their properties have enabled application in the field of tissue engineering, (bio)sensors, supercapacitors, solar panels, corrosion inhibitors, batteries, and many others. One of the essential representatives of conductive polymers is poly (3,4-ethylenedioxythiophene) (PEDOT) whose required properties can be tailored by grafting different side branches by atom transfer radical polymerization (ATRP). For this purpose, it is necessary to synthesize an ATRP macroinitiator containing easily reactive sites, so the first step is to synthesize 2-(thiophen-3-yl) ethyl 2-bromo-2-methylpropanoate (ThBr) which is introduced into the structure of the PEDOT polymer to obtain a macroinitiator functionalized with reactive bromine. In this paper, PEDOT ATRP macroinitiators in molar ratios of ThBr and EDOT monomers from 1:0,2 to 0,2:1 were synthesized by chemical oxidation polymerization to determine the reactivity ratio of monomers. In addition, ATRP macroinitiators with a 1:1 ratio of ThBr and EDOT were synthesized with the synthesis of 8, 16, 24 and 48 h to gain insight into the influence of synthesis duration on reaction yield and molar mass. Characterization of the obtained samples was performed by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), gel permeation chromatography (GPC), and nuclear magnetic resonance (NMR) spectroscopy. The results of the FTIR analysis showed that the synthesis of ThBr monomers and PEDOT macroinitiators of different composition was successfully performed except for the ThBr:EDOT 0,2:1 sample. TG analysis showed that the time of the synthesis does not affect the thermal stability of synthesized samples, while NMR analysis confirmed the expected structures of the synthesized samples and found that the theoretical reactivity ratios are approximately equal to the ratios obtained from the response surfaces of the inherent signals.