Effects of different reaction mediums on ring opening polymerization of poly(ε-caprolactone) by lipase
This work examined the effects of reaction conditions on ring opening polymerization of poly(ε-caprolactone) (PCL) by Candida antarctica lipase B (Novozym 435) as the catalyst. Different reaction mediums were obtained by changing of temperature, reaction time and solvent types simultaneously. The main purpose of this study was to observe molecular weight distribution, conversion rates, and thermal behaviors of PCL and to find the highest molecular weight in enzymatic reaction conditions. Three different reaction temperatures and solvent types were studied in this work. Reactions were carried out at 40, 60 and 80°C and n-hexane, toluene and diisopropyl ether were used as solvents. One more reaction series were done for toluene solution at 30°C. Moreover, experiments were undertaken at seven different time periods. During all the reactions, monomer, solvent, and enzyme concentrations were not changed. For 1 ml monomer/solvent solution (0.44 M monomer and 0.56 M solvent), 10 mg lipase were used in the experiments. All samples were analyzed by gel permeation chromatography (GPC) and hydrogen nuclear magnetic resonance (1H-NMR) to obtain molecular weights, conversion rates, and chemical structures. Fourier transform infrared spectroscopy (FTIR) analysis was performed to determine chain structures of PCL samples. Thermal behaviors of samples were analyzed by differential scanning calorimetry (DSC) to examine and compare polymers with each other.
Keywords: Candida antarctica lipase, enzymatic ring-opening polymerization, polycaprolactone, biopolymers