Preparation Of Molecularly Imprinted Polymer Microspheres With Hydrophilic Surfaces And Studies On Their Properties

Molecularly imprinted polymers (MIPs) have attracted significant interest in recent years due to their excellent affinity and selectivity as well as their high stability. The aim of this thesis is to prepare MIP microspheres with surface-immobilized hydrophilic polymer brushes via using controlled/"living" radical polymerization technique. It is expected that the introduction of the hydrophilic polymer shells can form efficient hydrophilic protection layers on the surfaces of the MIP microspheres, which can enhance the surface hydrophilicity of the MIPs and reduce their nonspecific adsorption towards the templates in aqueous solutions, thus leading eventually to MIPs directly suitable for the analyses of aqueous samples. The dissertation presents the following main points:1. A novel and convenient way is described for the preparation of MIP microspheres with surface-immobilized ATRP initiating groups, i.e., atom transfer radical precipitation polymerization (ATRPP) approach (including normal and reverse ATRPP). ATRPP provides MIP microspheres with obvious molecular imprinting effects towards the template, fast template binding kinetics and appreciable selectivity over structurally related compounds. The obtained MIP microspheres were characterized with SEM, FT-IR, elemental analysis, nitrogen adsorption experiments and HPLC. The living chain propagation mechanism in ATRPP results in MIP spherical particles with diameters (number-average diameter Dn≈3μm) much larger than those prepared via traditional radical precipitation polymerization (TRPP). In addition, The MIP microspheres prepared via ATRPP have also proven to show significantly higher high-affinity binding site densities on their surfaces than the MIP generated via TRPP, while the binding association constants Ka and apparent maximum numbers Nmax of the high-affinity sites as well as the specific template bindings are almost the same in the two cases. Furthermore, the presence of surface-immobilized reactive functional groups on the obtained MIP microspheres allows their further surface modification. 2. The first application of Atom Transfer Radical "Bulk" Polymerization (ATRBP) in molecular imprinting is described, which provides molecularly imprinted polymers (MIPs) with obvious imprinting effects towards the template, very fast binding kinetics, and an appreciable selectivity over structurally related compounds. In comparison with the MIP prepared via the normally used traditional "Bulk" free radical polymerization (BFRP), the MIPs obtained via ATRBP showed somewhat lower binding capacities and apparent maximum numbers Nmax for high-affinity sites as well as quite similar binding association constants Ka for high-affinity sites and high-affinity site densities, in contrast with the previous reports (e.g., nitroxide/ iniferter-mediated "bulk" polymerization provided MIPs with improved properties). We explained the phenomena by the experiment of gelation.3. Two strategies have been developed for the preparation of water-compatible MIPs by the facile surface-grafting of poly (N-isopropylacrylamide) brushes from the MIP particles either via surface-initiated ATRP (grafting from method) or Michael addition reaction (grafting to method). The presence of hydrophilic polymer brushes on the MIP particles has been confirmed with FT-IR, elemental analysis, the weight increase of the MIP particles as well as the dispersion experiment. The equilibrium binding results demonstrate that this polymer brushes-grafting approach is highly efficient for the preparation of water-compatible MIPs.