Synthesis And Application Of Supermacroporous Cryogels With High Surface Area

Porous polymeric materials are used in many fields ranging from packing materials for chromatography, supports for catalysts, scaffolds for growth of biological cells and tissues, to absorbents, cheap sensors, drug delivery vehicles and 3D batteries. Cryogel is a type of polymer that is obtained by cryo-polymerization at freezing temperature. Typically, cryogels possess supermacropores that lie normally in the range of several micrometers to several hundred micrometers in pore size, and are linked to form interconnected porous structure that is in favor of mass transfer. Most of literature focused on synthesis and application of hydrophilic cryogels, where ice crystals were used as porogen templates. In view of problems of cryogels, high melting point of organic solvents such as acetic acid and dimethyl sulfoxide are chosen as the porogen instead of ice crystals to prepare supermacroporous hydrophobic cryogels. After that, cryogels are treated with the post crosslinking method to enhance the specific surface area.In this dissertation, the main contents as follows:1. Synthesis of hydrophobic poly(lauryl methacrylate-divinylbenzene)(LMA-DVB) cryogels with supermacroporous structure: Acetic acid is of extensive solubility for most monomers, and its melting point is 16.6 oC. Thus acetic acid is suitable used as solvent and porogen for cryo-polymerization. Several factors that affected morphology and pore structure of cryogels, including polymerization temperature, ratio of monomer and crosslinker, and porogen content, were investigated. In the range of 60 to 90 vol% of acetic acid, polymerization at ambient temperature gives rise to particulate polymers in beaded or amorphous shape, while polymerization at 4 oC, lower than the melting point of acetic acid(16.6 oC), leads to the formation of cryogel-like monoliths with supermacroporous structure, which is mainly ascribed to cryo-concentration effect. According to the measurements by scanning electron microscopy and mercury intrusion porosimetry, the dried samples are supermacroporous with pore size mainly ranging from several micrometers to several hundred micrometers, which can be feasible for rapid mass transfer. The forming cryogels display a superfast responsiveness to organic solvents, possibly stemming from their supermacroporosity and distinctive hydrophobicity.2. Synthesis of supermacroporous PDVB cryogels with high specific surface area: In this part, supermacroporous cryogels are polymerized with divinylbenzene as monomer, dimethyl sulfoxide(melting point 18.45 oC) as solvent and porogen. Two kinds of post-crosslinking including radical initiated reaction and Friedel-Crafts reaction are chosen to improve the specific surface area of cryogels. The morphology and the pore structures of the cryogels are investigated using mercury intrusion, nitrogen adsorption and fourier transform infrared spectroscope. The results indicated that both of the two post-crosslinking methods effectively increased the specific surface area of the original cryogels. Especially, the cryogel that was post-crosslinked by Friedel-Crafts reaction, possessed 1214 m2/g of specific surface area, which is about 8.65- fold compared to that of the precursor.3. Green synthesis of polymeric microspheres that are monodisperse and superhydrophobic via quiescent redox-initiated precipitation polymerization:By virtue of simple quiescent redox-initiated precipitation polymerization, poly(lauryl methacrylatedivinylbenzene) microspheres are prepared. By scanning electron microscope, fourier transform infrared spectroscope and elements analysis, the effects of monomer content, crosslinking degree, initiator content on the morphology of the microspheres are investigated. Monodisperse microspheres bearing exceptionally low polydispersity index below 1.012 are obtained with a monomer concentration of 20 vol% in acetic acid at ambient temperature. Superhydrophobic surfaces with water contact angles around 160° are successfully fabricated by dip-coating and deposition of the highly monodisperse microspheres onto glass substrates.