Preparation And Characterization Of Monolithic Cryogel Enhanced With Carboxylic Acid Molecularly Imprinted Microspheres

Cryogel is a kind of interconnected porous material with sizes from severl to hundreds ofmicrons. It has become a new class of promising separation media for separation andpurification of nano and micron-sized biological particles. Usually, cryogel is prepared bycryo-radical polymerization at sub-zero temperture with ice crystals as porogen.The selected monomers require not only good solubility in water but also relatively rapidpolymerization rate at sub-zero temperature, which limites the range of monomer andcrosslinker. Low mechanical strength and few option of monomer for preparation of cryogelsare main obstacles for their application and development. The mechanical strength, theadsorption capacity and the adsorption selectivity of cryogel are the key problem to be solvedat present.Herein, this dissertation proposes a new way by a combination of molecular imprintingtechnique and cryogel technique to synthesize molecularly imprinted microspheres/cryogelcomposite monolith using dimethyl sulfoxide (DMSO) as a solvent and dispersant instead ofwater. Since DMSO is of low melting point (18.45oC) and can not only miscible with waterbut also dissolve most organic solvents with a wide range of solubility, both water-solublemonomers and oil soluble monomers can be chosen for synthsis of cryogels. The maincontents are as follows:1: A series of supermacroporous cryogels are polymerized with methacrylic acid asfunctional monomer, trimethylol propane trimethacrylate (TRIM), ethylene glycoldimethacrylate (EDMA), poly ethylene glycol diacrylate (PEGDA) as a crosslinking agentand DMSO crystals as porogens. The effects of polymerization temperature, types ofcrosslinking agent, and the functional monomer (MAA) contents on the pore structure of theresultant cryogels were investigated by scanning electronic microscope (SEM), mercuryporosimetry and measurement of the water content. The impact of preparation conditions onthe mechanical properties of cryogel was investigated by a material compression experiment.The separation of proteins was examined by equilibrium and chromatographic test. Theresults indicated that nano and micro-sized hierarchical porous cryogels could be obtained bycryo-copolymerization of MAA with the above three crosslinking agents using DMSO crystals as porogens. The pore size distribution of cryogels is dependent on inputs ofmethacrylic acid and types of crosslinking agent. Functional monomer (MAA) is a key factorin the formation of hierarchical porous structure of cyrogel. The resultant cryogels withhierarchical porous structure exhibited strong mechanical strength. The cryogel monolith canbe directly used as column media for separation of a protein mixture.2: Molecularly imprinted polymer/cryogel composites were prepared by combiningtechnologies of molecular imprinting and cryogel. Core-shell molecularly imprintedmicrospheres were obtained by using a surface imprinting method. Firstly, theepoxy-containing mcirospheres were obtained by solvothermal precipitation polymerizationusing divinylbenzene (DVB) and glycidyl methacrylate (GMA) as monomers. Secondly, β-structure of amino alcohols on microspheres were obtained by ring-opening reaction ofisopropylamine (IPA) with epoxy groups. Then, the naproxen molecularly imprintedcore-shell microspheres were obtaied by reversible addition-fragmentation chain transfer(RAFT) radical polymerization with s-naproxen as template and divinylbenzene ascrosslinking agents. The molecularly imprinted microspheres displayed a good adsorptioncapacity toward the template molecules by Scatchard analysis. The molecularly imprintedpolymer/cryogel composites were then prepared with by cryo-polymerization using DMSO assolvent and dispersant. The results showed that the embedded naproxen-imprintedmicrospheres in the cryogel enhanced the molecular recognition of the cryogel monolithtoward the template molecule.