Autopolymerization of 2-bromo-3-methoxythiophene, analysis of reaction products and estimation of polymer structure

Abstract

The study concerning the physical and chemical properties of thiophene derivatives has received much attention because they are incorporated in natural products, medicines, functional materials, and photoresponsive dyes. The autopolymerization reaction is one of the synthesis methods of polythiophenes using halogenated thiophene derivatives. In this paper, we analyzed the products and reaction mechanism of the polymerization reaction of 2-bromo-3-methoxythiophene by investigating the gas, liquid, and solid states using UV-Vis, electron spin resonance (ESR), gas chromatography/mass spectrometry (GC/MS), elemental analysis, NMR, and FT-IR spectroscopy. Consequently, we found a side reaction of the autopolymerization reaction and estimated that the polymerization reaction mechanism occurred in multiple steps. When we employed the brominated alkoxythiophene as a monomer, hydrogen bromide gas was generated to act not only as a catalyst of the polymerization reaction but also as an acid to cleave the alkoxyl group. The results provide useful information for the design of monomers via autopolymerization. The mechanism of intense autopolymerization reaction of 2-bromo-3-methoxythiophenes spewing brownish gas was clarified from UV-Vis, ESR, GC/MS, elemental analysis, NMR, and FT-IR spectroscopy. The reaction contained the formation of the hydrogen bromide gas during the autopolymerization. The gas induced the cleavage of the methoxy group on the thiophene ring to form the methyl bromide gas as the side reaction. This work provides an important guide for the application of the autopolymerization of thiophene derivatives to design new polymer materials.