Porous Polyurea Prepared By Precipitation Polymerization And Its Application In Enzyme Immobilization

In this work, porous polyurea(PPU) with functional amine groups was prepared via one-step precipitation polymerization of toluene diisocyanate(TDI) in H2O-acetone binary solvent. PPU microstructure was characterized using different instrumentation, including nuclear magnetic resonance(NMR, 1H and 13C), X-ray Diffraction(XRD) and Fourier transform infrared spectroscopy(FTIR). Thermal properties of PPU were also tested. PPU as-prepared has a specific surface area of 161.68 m2·g-1, a porosity of 71.77% and a pore volume of 2.20 cm3·g-1. Pores with size varying from 2 nm to 1000 nm are present, with the pore size mainly presented between 10 μm and 40 μm. PPU is analyzed by FTIR, the presence of characteristic groups in the PPU is all confirmed. These analyses show that TDI is full reacted and polyurea was effectively obtained. NMR tests confirm also that PPU is consisting of short polyurea chains with degree of polymerization of about 15. The presence of crystallinity in PPU is further confirmed by XRD, which shows three diffraction peaks. Through Bragg equation, corresponding interplanar spaces owing to different hydrogen-bonding and associated polymer chain conformation are depicted. TGA analysis demonstrates that PPU is of high thermal stability, and no degradation is seen before 270 °C. Through the imination of nitrobenzene formaldehyde with amine groups on PPU, density of amine on PPU surface is determinate, and influences of the nitrobenzene formaldehyde concentration and of reaction time on the results were studied. When the reaction time is 4 h, the molar ratio of aldehyde and amine groups are not less than 42.7, amine density of 9.89×10-8 mmol/cm2 was obtained.Fluorescent pseudomonas lipase(PFL) was immobilized on glutaraldehyde-activated PPU by covalent binding. Impact of solvent pH and GA concentration in the process were studied, the effect of concentration of free lipase on immobilized amount and the activity of the immobilized lipase was also explored. Thermal stability of the free and immobilized enzyme at 30 °C and 40 °C was compared. A higher stability for the immobilized enzyme was observed. The retained activity of the immobilized enzyme is 70% after repeated use in catalytic reaction.Immobilized enzyme was tested as a chiral biocatalyst for the resolution of racemic(R,S)-1-phenylethanol. Under the opmized condition(eep>99.5%, E>200), a conversion of 49.7% for the substrate was achieved with the immobilized enzyme as catalyst, whereas the highest conversion of substrate was limited to 41.9% with the free enzyme as the catalyst. That indicates an obvious increase in the enzyme activity and the enantioselectivity of the immobilized lipase. After five times of repeated use of the immobilized enzyme, the enantioselectivity was practically kept the same(eep>99.5%, E>200 with conversion of 46.4% for phenylethanol), a slight decrease in its activity was detected.