Study On Preparation And Characteristic Of Polymeric Particles With Unusual Morphology

Poly(N-isopropylacrylamide) (PNIPAAm) macromonomer with a styrol end group wasprepared by free radical polymerization of NIPAAm and end capping reaction. The properties ofPNIPAAm macromonomers, such as structures, molecular weight and molecular weight distributionwere characterized by Infrared Spectra (IR), Gel Permeation Chromatography (GPC) and NuclearMagnetic Resonance (NMR). Then PNIPAAm grafted poly(acrylonitrile /styrene)(PNIPAAm-g-PAN/PSt) particles in nanometer scale can be prepared by one-step method based onthe dispersion copolymerization of PNIPAAm macromonomer with AN/St monomers inethanol/water mixed solvents. The morphologies and diameter of the particles were characterizedby Scanning Election Microscopy (SEM), Transmission Election Microscopy (TEM) and LaserLighter Scattering (LLS). It showed that the AN monomer play a key role in the formation ofunusual particles: the morphology of particles can be changed from "pineapple" to "sphere" byvarying the amount of AN or ratio of AN to St. The reaction parameters such as macromonomerconcentration, initiator concentration, solvent composition and polymerization temperaturesimilarly affect morphologies, size and size distribution of final particles. Also the resultingPNIPAAm-g-PAN/PSt particles had a thermosensitive property.Poly(ethylene glycol)(PEG) macromonomer with a methacryloyl end group was selected asreaction stabilizer. The poly(ethylene glycol) (PEG) grafted polyacrylonitrile/polystyrene(PEG-PAN/PSt) polymeric particles were prepared by dispersion copolymerization of AN with St inthe presence of PEG macromonomer in ethanol/water mixed solvents (vol/vol=7/3) at 60℃ for 24hby using 2,2'-azobisisobutyrnitrile(AIBN) as a free radical initiator. The factors influencing themorphology and the size of particles such as the concentration and molecular weight ofmacromonomer, the concentration of total monomers, initiator concentration, polymerizationtemperature and solvent composition were investigated by TEM and LLS. The results showed thatthere is a quantitative relation between the particle size and the fleet ratio (the macroscopic weightratio of macromonomer to monomer): Wm/Wp = 6.20*10-2Rh-3.49, that is to say, the surface areaoccupied by each PEG macromonomer is nearly a constant.The control release of propafenone was studied by using the PEG-PAN/PSt particles withunusual morphology as carrier. The kind of this medicine is not very suitable for this drug releasesystem.