Synthesis and characterization of imine-functionalized polyphenol via enzymatic oxidative polycondensation of a bisphenol derivative

Abstract

Enzymatic oxidative polycondensation of a new bisphenol derivative 3,3′-((1E,1′E)-(1,3-phenylenebis(azanylylidene))bis(methanylylidene))diphenol, (3,3′-PBAMD), using horseradish peroxidase (HRP) enzyme and hydrogen peroxide (H2O2) oxidizer for initiation of the reaction, has been investigated in an equivolume mixture of an organic solvent (acetone, methanol, ethanol, dichloromethane, 1,4-dioxane and tetrahydrofuran) and phosphate buffer (pH = 5.0, 6.0, 7.0, 8.0 and 9.0) at different temperatures under air for 24 h. The resulting polymer, poly(3,3′-PBAMD), was characterized using ultraviolet–visible (UV–Vis), Fourier transform infrared (FT-IR), 1H nuclear magnetic resonance (NMR), gel permeation chromatography (GPC) and thermogravimetric (TGA) analyses. Effects of solvent system, reaction temperature and pH on the polymerization have been investigated with respect to the yield and molecular weight (M n) of the product. The optimum reaction condition in terms of the highest yield (81 %) and molecular weight (M n = 10,500 g/mol, DP ~33) was achieved in an equivolume mixture of tetrahydrofuran/pH 7.0 phosphate buffer medium at 25 °C. Polymerization involved hydrogen elimination from the monomer, and terminal units of the polymer structure consisted of phenolic hydroxyl (–OH) groups at the ends. The polymer is mainly composed of a mixture of phenylene and oxyphenylene units according to 1H NMR and FT-IR analyses. The resulted product has shown relatively high thermal stability against thermal decomposition, and 35 % of the initial weight of the sample (carbonaceous residue) remained after heating to 1000 °C.