Ersen Gokturk

Chemoenzymatic polycondensation of para-benzylamino phenol

Abstractpara-Benzylamine substituted oligophenol was synthesized via enzymatic oxidative polycondensation of 4-(benzylamino)phenol (BAP). Polymerization involved only the phenolic moiety without oxidizing the sec-amine (benzylamine) group. Chemoselective polycondensation of BAP monomer using HRP enzyme yielded oligophenol with sec-amine functionality on the side-chain. Effects of various factors including solvent system, reaction pH and temperature on the polycondensation were studied. Optimum polymerization process with the highest yield (63 %) and molecular weight (Mn = 5000, degree of polymerization ≈ 25) was achieved using the EtOH/ buffer (pH 5.0; 1: 1 vol. ratio) at 25°C in 24 h under air. Characterization of the oligomer was accomplished by 1H NMR and 13C NMR, Fourier transform infrared spectroscopy (FT-IR), gel permeation chromatography (GPC), ultraviolet-visible spectroscopy (UV-Vis), cyclic voltammetry (CV) and thermogravimetric analysis (TGA). The polymerization process involved the elimination of hydrogen from BAP, and phenolic-OH end groups of the oligo(BAP), confirmed using 1H NMR and FT-IR analyses. The oligomer backbone possessed phenylene and oxyphenylene repeat units, and the resulting oligomer was highly soluble in common organic solvents such as acetone, CHCl3, 1,4-dioxane, N,N-dimethylformamide (DMF), tetrahydrofurane (THF) and dimethylsulfoxide (DMSO). Oligo(BAP) was thermally stable and exhibited 5 % and 50 % mass loss determined by thermogravimetric analysis at 247°C and 852°C, respectively.

Polyglycolic acid from the direct polymerization of renewable C1 feedstocks

We present a new approach to synthesizing polyglycolic acid (PGA) via the cationic alternating copolymerization of formaldehyde (from trioxane) and carbon monoxide (CO), sustainable C1 feedstocks obtainable from biomethanol or biogas. This method constitutes an inexpensive and efficient pathway for the synthesis of PGA, circumventing the usual route requiring glycolide. PGA was successfully synthesized with yields up to 92% from trioxane, 800 psi of CO, and 1 mol% triflic acid (TfOH) initiator at 170 °C over three days. 1H NMR, 13C NMR, and FT-IR spectra of the polymer from CO and trioxane are identical to those of commercial PGA prepared via the ring-opening polymerization of glycolide—confirming the alternating microstructure. Although high copolymerization conversions were obtained, molecular weight analysis usually suggested the formation of oligomeric glycolic acid (OGA). High molecular weight PGA can be obtained via post-polymerization polycondensation of OGA catalyzed by Zn(OAc)2·2H2O. Alternatively, increased molecular weight PGA can be achieved by inclusion of glycerol as a branching agent during the C1 copolymerization.

Chemoenzymatic polymerization of hydrazone functionalized phenol

Hydrazone substituted oligophenol was synthesized via enzymatic oxidative polymerization of (E)-2-((2-phenylhydrazono)methyl)phenol. Enzymatic polymerization catalyzed by Horseradish peroxidase (HRP) enzyme and H2O2 oxidizer yielded oligophenol with hydrazone functionality on the side-chain. Effects of various factors including solvent system, reaction pH and temperature on the polymerization were studied. Optimum polymerization conditions with the highest yield (84%) and molecular weight (M n = 8 × 103, DP ≈ 37, PDI = 1.11) was achieved using MeOH/pH 6.0 buffer (1: 1 vol %) at 25°C in 24 h under air. Synthesized oligomer was characterized by 1H and 13C NMR, FTIR, UV–Vis spectroscopy, GPC, cyclic voltammetry and thermogravimetric analyses. The polymerization involved hydrogen elimination from the monomer, and terminal units of the oligomer structure consisted of phenolic hydroxyl (–OH) end groups. The oligomer backbone possessed phenylene and oxyphenylene repeat units. The resulting oligomer was completely soluble in common organic solvents. The oligomer was thermally robust and exhibited 5% mass loss at 375°C and 50% mass loss at 440°C.