Preparation And Characteristic Of Molecular Imprinted Polymers In Supercritical Carbon Dioxide

Carbon dioxide is inexpensive, nontoxic, and non-flammable, and it has an easily accessible critical temperature of 31.1°C and critical pressure of 7.38 MPa, and it has both liquid and gas like characteristic. So the use of scCO2 as an alternative to traditional aqueous and organic solvents has attracted much attention in the fields of extraction, polymer synthesis and materials processing. The present study investigates the feasibility of using scCO2 as a polymerization medium for the following research work:(1) Cross-linked Poly (N-isopropylacrylamide) microparticles using ethylene glycol dimethacrylate as cross-linker were prepared in scCO2. It is possible to obtain uniformly dispersed particles by changing the initial concentrations of initiator, cross-linker and pressure as well as reaction time. The polymers were obtained in high yield as dry, fine and free flowing materials directly from the reaction vessel; The network showed not only easily swelled in deionized water but have relatively high swelling in pure ethanol. This shows the potential of the polymer in bio-medical applications.(2) Cross-linked Poly (4-vinylpyridine) (P4-VP) were synthesized in scCO2. The slight yellow, dry, fine powders were obtained directly from precipitation polymerization of 4-vinylpyridine (4-VP) in scCO2 with N, N/-methylenebisacrylamide as cross-linker. The effects of the reaction pressure, cross-linker ratio, initiator concentration, and reaction time were investigated. It was found that under the condition of 14 MPa and 70°C the cross-linked P4-VP microparticles were generated in scCO2, in yield of 80%, using higher cross-linker concentrations.(3) Furthermore, Molecularly Imprinted Polymers (MIPs) for (S)-naproxen were prepared in supercritical carbon dioxide. In the present work, (S)-naproxen was used as a model template, 4-vinylpyridine as a functional monomer, and Ethylene Dimethacrylate as a crosslinker. Compared with the nonimprinted polymers (NIPs), the MIPs displayed much higher (S)-naproxen uptake in acetonitrile. Scatchard analysis shows that two classes of binding sites were formed in the MIPs in the concentrations range studied. The calculated dissociation constant Kd1 and the apparent maximum binding capacities Qmax1 for the high affinity sites are 0.50 mmol L-1 and 25.5μmol g-1, while Kd2 and Qmax2 for the low affinity sites are 5.3 mmol L-1 and 82.2μmol g-1, respectively.