Controlled Synthesis Of Advanced Molecularly Imprinted Polymers And Study On Their Properties

Molecular imprinting technology is a versatile and straightforward method for the preparation of polymer receptors with tailor-made recognition sites. The resulting polymers are called molecularly imprinted polymers. Their easy preparation, low cost, high stability, and good molecular recognition ability make them highly promising in a wide range of applications such as separation and purification, immunoassays, biomimetic catalysis, organic synthesis, drug development and drug delivery. Herein, we first made a detailed comparison of the MIPs prepared via RAFT "bulk" polymerization (RAFTBP) and traditional radical "bulk" polymerization (TRBP). In addition, narrowly dispersed hydrophilic MIP nanoparticles were successfully synthesized via poly(2-hydroxyethyl methacrylate)(PHEMA)-mediated RAFT precipitation polymerization (RAFTPP), which proved to be compatible with real aqueous samples including river water, pure milk and bovine serum. Furthermore, a faicle, general, and highly efficient approach for the preparation of narrowly dispersed MIP microspheres with multiple stimuli-responsive was developed via the combined use of RAFTPP and successive surface-initiated RAFT polymerization. The detailed contents of this thesis are provided below:1. Bisphenol A and propranolol-imprinted polymers have been prepared via both RAFTBP and TRBP under similar reaction conditions, and their equilibrium binding properties were compared in detail for the first time. The chemical compositions, specific surface areas, equilibrium bindings, and selectivity of the obtained MIPs were systematically characterized. The experimental results showed that the MIPs with molecular imprinting effects and quite fast binding kinetics could be readily prepared via RAFTBP, but they did not show improved template binding properties in comparison with those prepared via TRBP, which is in sharp contrast to many previous reports. This could be attributed to the heavily interrupted equilibrium between the dormant species and active radicals in the RAFT mechanism because of the occurrence of fast gelation during RAFTBP. The findings presented here strongly demonstrate that the application of controlled radical polymerizations (CRPs) in molecular imprinting does not always benefit the binding properties of the resultant MIPs, which is of significant importance for the rational use of CRPs in generating MIPs with improved properties.2. The efficient synthesis of narrowly dispersed hydrophilic MIP nanoparticles with excellent specific molecular-recognition ability in real aqueous solutions, including river water and biological sample was reported. RAFTPP mediated by hydrophilic macromolecular (PHEMA) chain-transfer agents provided for the first time narrowly dispersed highly cross-linked MIP nanoparticles with surface-grafted hydrophilic polymer brushes in a facile one-pot approach. The MIPs were characterized by FT-IR, SEM, water dispersion experiments and static water contact angle experiments. The hydrophilic polymer brushes on the MIP nanoparticles significantly improved their surface hydrophilicity and led to their water compatibility. The chain length of the polymer brushes on the MIP nanoparticles had a significant influence on the compatibility of the nanoparticles with biological samples:only sufficiently long polymer brushes could act as an efficient protective layer to prevent the accumulation of proteins on the nanoparticle surface and thus enable the nanoparticles to function properly in such a complex milieu. The synthetic MIP nanoparticles are highly promising alternatives to biological receptors with great potential in many analytical applications (e.g., for environmental, food, and clinical analyses) and other areas.3. In this section, the facile and controlled synthesis of narrowly dispersed MIP microspheres with photo-/thermo-or photo-/thermo-/pH-responsive template binding properties in pure aqueous media is described. Narrowly dispersed "living" core polymer microspheres with surface-immobilized dithioester groups were firstly prepared via RAFTPP. The polymer microspheres were then successively grafted with an azobenzene (azo)-containing MIP layer and the thermo-responsive poly(N-isopropylacrylamide)(PNIPAAm) or thermo-/pH-responsive poly((N-isopropylacrylamide)-co-(2-(dimethylamino)ethyl methacrylate))(poly(NIPAAm-co-DMAEMA)) brushes via surface-initiated RAFT polymerization to provide the desired product. The successful grafting of the azo-containing MIP layer and hydrophilic brushes were confirmed by FT-IR, SEM, water dispersion experiments and static water contact angle experiments. The attachment of an azo-containing MIP layer onto the "living" core polymer beads with a narrow size distribution allows the direct generation of narrowly dispersed photo-responsive core-shell MIP microspheres. Moreover, the introduction of PNIPAAm or poly(NIPAAm-co-DMAEMA) brushes onto the core-shell MIP microspheres proved to not only significantly improve their surface hydrophilicity and lead to pure water-compatibility, but also provide the thermo-or thermo-/pH responsive layers toward external stimuli. It has demonstrated for the first time a facile and highly efficient approach to prepare narrowly dispersed MIP microspheres with multiple stimuli-responsive template binding properties in aqueous media. The advanced functional and smart MIPs have great potential in such applications as stimuli-responsive drug delivery and bioanalytical chemistry.