Bisphenol A Imprinted Polymer Spheres: The Preparation, Structure Control And Molecular Recognition Studies

Molecularly imprinted polymer(MIP)is a kind of tailor-made synthetic receptor materials with high affinity and selectivity towards target molecules,and it has aroused wide concern in solid phase extraction,chromatographic separation,biomimetic sensor,membrane separation,drug delivery and artificial antibody.Meanwhile,the morphology control of polymer microspheres prepared by heterogeneous polymerization in emulsion conditions and the influence of micro-nano structure on application performance are also research hot spots in recent years.However,the reports about the subtle structural control on MIP microspheres are limited,and the influence of the micro-nano structure on molecular recognition performance also needs further research.In this dissertation,we choose the endocrine disrupter of bisphenol A(BPA)as template molecules.MIP material including microspheres,multicore microcapsules,submicron and single hole hollow particles have been synthesized through different stragies based on Pickering emulsion and miniemulsion polymerization,respectively.We have systematically studied the synthetic variables as well as the influence of the microstructure of MIP on the molecular recognition performance.The main work is as follows:1.MIP microspheres with the mean size of 70 ?m have been prepared by Pickering emulsion polymerization.In the synthesis,the only stabilizer is silica particles prepared in our laboratory by Stober process.The template molecules hydrogen bonded with functional monomer were introduced into the reaction system.After polymerization,the silica particles and template molecules were removed by ultrasonic washing and soxhlet extraction,respectively.Finally,the clean MIP microspheres were obtained.The use of hydrophilic functional monomer of methacrylic acid(MAA)makes the surface of MIP microspheres be rich in carboxyl,which can improve the surface hydrophilicity of MIP microspheres.Therefore,the MIP could selectively rebind with the target compound from the water medium.The morphology of droplets and polymer spheres was observed by optical microscope and scanning electron microscope(SEM),respectively.The impact of silica addition on the sphere size and porogen addition on rebinding specificity was investigated in detail.The rebinding experiments indicate that the rebinding kinetics of MIP spheres conforms to the pseudo first order model,and the isothermal adsorption behavior conforms to the Langmuir model.The rate and equilibrium constants are 0.445×10-2 min-1 and 6.21×103 L mol-1,respectively.The apparent maximum binding sites number is 4.91 ×102 ?mol g-1.MIP has excellent selectivity judged by the imprinting factor of 3.60.2.MIP microcapsules with multicore structure have been successfully prepared by Pickering emulsion polymerization combined with the polymerization induced phase separation and the nucleation inducing effect of BPA.In the synthesis,4-vinylpyridine(4-VP),divinyl benzene(DVB),silica nanoparticles and hexadecane(HD)was employed as functional monomers,crosslinking monomers,stabilizer and phase separation agent,respectively.The impact of silica,HD and template dosage on the microstructure of the product was investigated in detail.The research shows that BPA could dissolve in the mixture of 4-VP and DVB fast,but not dissolve in the nonpolar solvent of HD.With the increase of conversion rate,the oversaturated BPA precipitated from the oil phase and served as the nucleation agent for propagating copolymer which was incompatibility with HD.Due to the phase separation between the copolymer and HD,the new polymer phase grew up at the interfaces of Pickering droplets and the interior crystal nucleus simultaneously.Finally,the microcapsules with multicore structure were obtained.The number and size of cores inside the shell could be adjusted by changing the amount of BPA or HD.The rebinding experiments indicate that the rebinding kinetics of MIP microcapsules conforms to the pseudo first order model,and the isothermal adsorption behavior conforms to the Langmuir model.The rate and equilibrium constants are 0.133 min-1 and 0.53×103 L mol.-1,respectively.The apparent maximum binding sites number of MIP is 100 ?mol g-1.The excellent selectivity of MIP microcapsules with the imprinting factor of 1.96 was verified by selective and competitive experiments.3.MIP particles with submicron size have been prepared by miniemulsion polymerization.In the synthesis,hydrophilic MAA and hydrophobic EGDMA were adopted as functional monomer and crosslinker,respectively.The influence of the ratio between MAA and EGDMA on the size,size distribution and rebinding selectivity of MIP particles was investigated.Meanwhile,the structures and surface morphologies of MIP particles were characterized by TEM and SEM,respectively.The images indicate that MIP particles with rough porous feature have an average size of 138 nm.The high density of carboxylic groups situated on particle surface was verified through the conductivity titration experiment.The MIP could selectively rebind with the target compound from the water medium.The rebinding experiments indicate that the rebinding kinetics of MIP particles conforms to the pseudo second order model,and the isothermal adsorption behavior conforms to the Bi-Langmuir model.The rate constant is 3.364×10-3 g ?mol-1min-1,and the the half equilibrium time of t1/2 is 1.66 min.The Scatchard plot indicates that the binding sites on MIP possess different affinities towards BPA.The affinity constants of high-and low-affinity sites are 39.5 and 5.83 L mmol-1,respectively.The excellent rebinding selectivity of MIP particles with the imprinting factor of 1.87 was v.erified by selective and competitive experiments.4.MIP particles with single hole hollow structure have been prepared by miniemulsion single step swelling polymerization.Polystyrene(PS)has been introduced into the miniemulsion polymerization system,which is used as the seed for the subsequent monomer swelling to tailor the following polymerization.The influence of the composition of monomer and crosslinker on the particle structure was investigated by SEM and TEM.Under the proper ratio of monomer and crosslinker,the single hole hollow structure could be obtained in both of the systems of methyl methacrylate(MMA)/DVB and MAA/EGDMA.However,their morphological characteristics as well as the BPA recognition capabilities have obvious difference.The single hole hollow structure is attributed to the polymerization induced phase seperation,during which the addition of template molecules does not have effect on the morphology.But only the system of MAA/EGDMA presented the rebinding selectivity towards BPA in water medium.The rebinding experiments indicate that the rebinding kinetics of MIP particles conforms to the pseudo second order model,and the isothermal adsorption behavior conforms to the Bi-Langmuir model.The rate constant is 1.255×10-3 g ?mol-1min-1,and the t1/2 is 4.35 min.The Scatchard plot indicates that the binding sites on MIP possess different affinities towards BPA.The affinity constants of high-and low-affinity sites are 67.0 and 4.02 L mmol-1,respectively.The excellent rebinding selectivity of MIP particles with the imprinting factor of 1.98 was verified by selective and competitive experiments.