Study On Preparation And Characteristic Of Swollen Polymeric Aggregate

The poly(ethylene glycol) macromonomers (PEG) with different molecular weight weresynthesized by end capping reaction. The properties of macromonomers, such as molecularweight, molecular weight distribution and content of vinyl group in polymer end were characterizedby Gel Permeation Chromatography (GPC), Infrared Spectra (IR), and Ultraviolet Spectra (UV).The nanospheres with core/shell structures were prepared by dispersion copolymerization ofSt-PEG macromonomer with n-butyl methacrylate (MBA) were synthesized in ethanol/water mixedsolvents. It was found that the solvophilic/solvophobic balance between the copolymers andmediums had great effect on the formation of nanospheres. It had become clear that the obtainedpolymer dispersion form four kinds of states: clear solution, particle dispersion (milky solution),milky solution with gel/precipitation and gel with varying BMA concentration and water content inmixed medium. The particle size and morphology of obtained nanospheres were characterized bythe transmission electron microscopy and laser lighter scattering. It showed that nearlymonodispersed nanospheres were obtained. It also found that the solubility parameter of the mixedsolvent has effect on the molecular weight of copolymer and the particle size and its distribution ofobtained nanospheres. Through the hydrodynamic study of the process of the nanosphere formation,the effects of the molecular weight of the macromonomers, the composition of solvent andconcentration of initial BMA, initiator, and macromonomer on the particle size were investigated.The hydrodynamic radius (R_h) of resulting nanospheres followed the relationship: Rh = K[I]^{-0.12±0.01}[Macromolecule]^{-0.65±0.03}[BMA]^1.13±0.05, where [I], [Macromolecule] and [BMA] are the initialconcentration of initiator, St-PEG macromolecule and BMA, respectively, and K is constant. Whenthese reaction parameters were properly chosen, the particle size could be controlled in a range fromca. 40 nm to 750 nm in diameter. It was found that nanospheres swelled in ethanol/water dispersionmedia and the degree of swelling responded sensitively to solvent composition changes. Through the static light scattering measurement, it obtained that the molecular weight (Mw), thegyration radius(Rg) and the second Viral coefficient(A2) of the poly(γ-glutamic acid)( γ-PGA)chain were 3.332×10⁵ g/mol, 59.25nm and 4.910×10^-6 molL/g² respectively. Through the analysisof the ratio of Rg/Rh (hydrodynamic radius that was obtained by the hydrodynamic light scatteringmeasurement) in dilute solutions (below the critical overlap concentration), with different γ-PGAconcentration, it was confirmed that the γ-PGA chain showed the characteristic of stiff chain0.1mol/L NaOH. The hydrodynamic light scattering measurement was also used to trace thedegradation behavior of the γ-PGA chain in 0.1mol/L NaOH at 50oC. The study showed that thedestruction of the γ-PGA chain did not occur at the random sites of the poly chain. The destructionof the poly chain should start at the end groups of the γ-PGA chain. Using 1,4-Butandiol diglycidyl ether (BGDGE) or Ethylene diglycidyl ether(EGDGE) ascrosslinker and tetraethylammonium bromide as catalyst, the γ-PGA gel was synthesized in DMSOat 60oC for 48h. The effect of reaction condition on the swelling ratio of resulting hydrogel wasdetermined. It was also found that the concentration and the value of the adding ion had a greateffect on the swelling ratio of the hydrogel. In this study, the Ibuprofen was used as a model medicineto explore the possibility of the hydrogel being used as a carrier as drug release system.