Horseradish peroxidase-catalyzed polymerization of ortho-imino-phenol: Synthesis, characterization, thermal stability and electrochemical properties

Abstract

Enzymatic polymerization of phenols has been investigated extensively over the last decades. However, involving imine functional group in the side chain of an oligophenol and its effect on polymerization is poorly understood. Therefore, the influence of the imine functionality in the side chain of oligophenol for enzymatic polymerization is explored in this work. Ortho-imine substituted phenol, (E)-2-((p-tolylimino)methyl)phenol (PTIMP), was enzymatically polymerized using horseradish peroxidase (HRP) enzyme in aqueous organic solvents and hydrogen peroxide (H2O2) as an oxidant. Different parameters (solvent system, pH and reaction temperature) on polymerization were investigated. EtOH/pH 6.0 buffer (50:50 vol.%) at 25 °C in 24 h under air was found to be the optimum polymerization condition with 65% of yield and Mn = 6100 g/mol (DP ≈ 29, PDI = 1.09). Polymerization of PTIMP in the presence of HRP enzyme catalyst leads to the formation of an oligophenol containing phenylene and oxyphenylene repeat units. The resulting oligophenol is soluble in most of the organic solvents. Characterization of oligo(PTIMP) was achieved by NMR, UV–Vis, CV, FT-IR spectroscopy and thermogravimetric analysis. Keywords: Horseradish peroxidase, Enzymatic polymerization, Hydrogen peroxide, Imine functionality, Phenol