Synthesis Of Core-Shell Structure Thermoresponsive Microgels Cross-Linked With Poly(Acryloyloxyethyl/Hydroxyethyl)-DL-Asparagine

Core-shell structure microgels, a kind of polymeric composite particle, have a unique structure and were prepared by the gelation on the outer of core. The synthesis of thermoresponsive core-shell structure microgels is a great challenge in the fields of synthetic chemistry and materials science, because of the request of uniform, high swollen (or shrunken) ratio and degradability. In this paper, a novel cross-linker, poly(acryloyloxyethyl/hydroxyethyl)-DL-asparagine (PAEHEA), which is biodegradable and biocompatible, was synthesized by microwave irradiation. The poly-N-isopropylacrylamide (PNIPAAm) thermoresponsive microgels were prepared via free-radical precipitation polymerization with the cross-linker PAEHEA and monomer N-isopropylacrylamide (NIPAAm) as materials. Using the dispersion of microgels as seeds, a series of core-shell structure thermoresponsive microgels were synthesized, and their thermoresponsibility, volume phase transition temperature (VPTT), particle size and size distribution, the kinetics of swollen-shrunken and degradability were investigated. In addition, the morphology of microgels was characterized by TEM and AFM spectroscopy.1,The cross-linker PAEHEA was synthesized from the chemical modified polyasparagine, which was prepared with the microwave irradiation method using the maleic anhydride and ammonia as materials, and was characterized by FT-IR and 13C-NMR. The optimum conditions of synthesis were obtained.2,The PNIPAAm thermoresponsive microgels were prepared via free-radical precipitation polymerization with NIPAAm and PAEHEA as materials. The effects of the concentrations of monomer (NIPAAm), cross-linker (PAEHEA), initiator (APS) and surfactant (SDS) on the mean diameters of the microgels and their VPTT were carried out. The results showed that all of them affected the VPTT of the microgels except the concentration of monomer.3,A series of core-shell structure micogels was prepared by precipitation polymerization, and its thermoresponsibility and volume phase transition (VPT) behaviors were studied by measuring the transmittance. Increasing the dosages of shell materials, the transmittance of microgels decreased gradually and the VPT behaviors became inapparent. While decreasing the dosages of PAEHEA, the transmittance of microgels decreased and the VPT behaviors became inapparent.4,The particle size and the kinetics of swollen-shrunken of core-shell structure micogels were measured by dynamic light scattering (DLS) method. The results displayed that the more shell materials or monomer were used, the smaller particle size and the higher shrunken ratio were. With the increasing of dispersions temperature, the particle size decreased slowly and when the temperature was high above VPTT, the particles shrunk rapidly. The curves of size distribution were V-type and the rock bottom's temperature, about 30.0 ~ 31.5 oC, coped with the VPTT.5,The PNIPAAm microgels and core-shell structure micogels, cross-linked by the PAEHEA, showed excellent degradability with the test of trypsine.6,TEM analysis indicated that the microgels dispersions had excellent stability and monodispersity, and the core-shell structure could be observed and proved. AFM analysis also indicated that the dispersions had uniform particle sizes, and the microgels of core-shell structure had a more clear image.