| Smart nanogels can be rapidly responsive to the environmental conditions with temperature, p H value, biomolecule or electric field,etc. Polyethylene glycol(PEG), a kind of excellent biocompatible material, has been widely used in drug delivery and tissue engineering, gene transfer, immune precipitation analysis, etc. PEG itself has temperature responsiveness, but the lower critical solution temperature(LCST) is too high(about 100 oC), which greatly limits its widely application. Nanogel with fast responsiveness, biocompatibility and sensitivity to the body temperature is the research hotpot of smart hydrogel.The prepared poly(polyethylene glycol diacrylate/methacrylic acid(PEGDA/MAA) nanogels appeared a volume phase transition behavior under the body temperature, which led to a series of work. In this dissertation the main research content is listed as follows:1 Poly(PEGDA/MAA) nanogels were prepared by aqueous precipitation polymerization with MAA as functional monomer, PEGDA(Mw=258, 575, 700) as crosslinking agent, ammonium persulfate(APS) as initiator. The effects of monomer loading, crosslinking degree and crosslinking agent type on the synthesis were investigated by the scanning electron microscopy(SEM), proton nuclear magnetic resonance(1H NMR) and potentiometric titration method. The effects of MAA content, p H and salt concentration on the LCST were investigated. The experimental results showed that the stable nanogels could be obtained when the monomer loading decreased below 0.2 wt%. The introduction of MAA is the key factor in the formation of stable nanogels. The LCSTs of hydrogels decreased with the increase of MAA content and salt concentration and the decrease of p H value. The LCST of poly(PEGDA/MAA)(40/60, mol/mol) nanogels in a simulated gastric liquid was determined at 35 oC, close to the body temperature. The loading and release of 5-FU were investigated. The release rate in the simulated intestinal liquid(45.5%) is lower than that in the simulated gastric liquid(82.4%).2 In order to enhance the monomer loading, the poly(PEGDA/MAA)(40/60, mol/mol) were prepared by solvothermal polymerization with MAA as functional monomer, PEGDA575 as crosslinking agent, APS as water phase initiator, azodiisobutyronitrile(AIBN) as oil phase initiator, and five solvents, i.e., water, ethanol, acetonitrile, acetic acid or dimethyl sulfoxide(DMSO) as solvent, respectively. The effects of solvent, reaction temperature and monomer loading on the synthesis were investigated. The effect of monomer loading amount on the temperature responsiveness was investigated. The experimental results showed that the stable dispersion can be obtained only with the ethanol as solvent. MAA contents in the copolymer were more close to the monomer loading ratio with the increase of monomer loading amount. Compared to the aqueous precipitation polymerization, the solvothermal polymerization resulted in 25 to 40 folds increase of the monomer loading. The LCSTs of poly(PEGDA/MAA) nanogel decreased with the increase of monomer loading amount(70-30 oC).3 The UCST behavior of poly(PEGDA/MAA) nanogel was investigated. Ethanol, acetonitrile, acetic acid and DMSO were chosen as solvent. The experimental results showed that the poly(PEGDA/MAA) nanogels displayed UCST of 43-58 oC in ethanol varying with the nanogel concentrations. The mechanism of UCST transition behavior was put forward. The solubility of polymer increased with the destroyed hydrogen bond, which induced the formation of nanoparticles at high temperature(60 oC);. The solubility of nanogels decreased with the increase of hydrogen bond between polymer chains at room temperature, which led to the formation of microsized particles.4 The effects of nanogel concentration and biomolecules(lysozyme and aspartic acid) on the self-assembly behavior of nanogel were preliminarily investigated. The experimental results showed that nanoparticles gathered to assemble microspheres(5.08 μm) with the increase of concentration of nanogel(2.5-5.0 mg/ml) at p H 1.0. The similar phenomena were observed with the increase of concentration of lysozyme and aspartic acid. This showed that the self-assembly behavior of nanogel could be attributed to the synergistic effect of hydrogen bonding, hydrophobic interaction and Van der Waals force. |
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