Study On Preparation And Performance Of PNIPAM/CS Microgels

Temperature-sensitive microgels have showed potential prospects in many areas because of their predominant characteristics, such as rapid responses and micro-sizes. In this study, appropriate monomers were choosen and prepared functional microgels such as temperature-sensitivity, functionality, biocompatibility and biodegradability. Moreover, the properties of microgels were invetigated systematically, which provided guidance for the application of drug slow-releasing of microgels.Based on the favorable properties of CS and temperature-sensitivity of N-isopropylmethacrylamide (NIPAM), copolymers of CS and NIPAM synthesized by surfactant-free emulsion polymerization possessed dual sensitive property of temperature and pH. The composition and microstructure of microgels were characterized by Fourier transform infrared spectroscopy (FT-IR) and 1H-nuclear magnetic resonance (1HNMR). The morphology and dispersity of microgels were observed by Scanning electron microscope (SEM) and Transmission electron microscope (TEM). The volume phase transition temperature (VPTT) of microgels was measured by Dynamic light scattering (DLS), Ultraviolet-visible spectroscopy (UV) and Differential scanning calorimeter (DSC). Meanwhile, effect of pH value on the VPTT of microgels and effect of salt concentration on the stability of microgels were estimated systematically. In addition, PNIPAM/CS particles with bigger size were prepared to make the load and release of drug carried out. The drug release ability of PNIPAM/CS particles was measured as a function of different temperature and pH.The research indicated that the graft copolymers of PNIPAM/CS were reacted more easily on the positions of C2-NH2 and C6-OH of CS. The results of FT-IR and 1HNMR demonstrated that the graft copolymerization had been performed. PNIPAM/CS microgels exhibited well monodisperse spheres with regular size. The periphery of the microgels was dense hairy coronal. The appearance revealed a core-shell nanostructure. but the core-shell boundary was not obvious. With increasing temperature, the size distribution of PNIPAM/CS microgels became narrow and the particle sizes became small. With increasing MBA cross-linker content, the particle sizes increased and the deswelling ratio decreased. With increasing CS monomer content, both the particle sizes and the deswelling ratio decreased.The VPTT of microgels M-Gel2, M-Gel4, M-Gel5 and M-Gel6 was 33℃,34℃, 34℃and 35℃respectively. The results of DLS measurement were consistent with the results of UV measurement. It indicated that PNIPAM/CS microgels possessed temperature-sensitive. The increase of the turbidity was attributed to the shrinkage of microgels rather than the aggregation of microgels. When CS was kept at a constant content, the VPTT of microgels increased with increasing MBA cross-linker content. When MBA was kept at a constant content, the VPTT of microgels increased with increasing CS content.The UV measurement indicated that the VPTT of microgels was affected with pH. The VPTT of microgels was shifted to lower temperature with increasing pH from 2 to 8, whereas the VPTT was at higher temperature as pH9. With pH increasing the particle sizes decreased firstly, and then presented an increasing tendency, while the turbidity increased firstly, and then presented a decreasing tendency. It showed that PNIPAM/CS microgels had obvious pH sensitivity.With increasing the NaCl concentration, the particle sizes of PNIPAM/CS microgels decreased firstly, and then presented an increasing tendency at 25℃. The critical NaCl concentration that induced flocculation of microgels M-Gel2 and M-Gel4 was 0.8mol/L around. The critical NaCl concentration that induced flocculation of microgels M-Gel5 and M-Gel6 was 1.4mol/L around. The flocculation of microgels wasn't induced by elevating the temperature under the lower NaCl concentration (0.02mol/L). As the NaCl concentration increased, the flocculation of microgels M-Gel2 and M-Gel4 took place at elevated temperature because of the colloidal unstablity. The critical flocculation temeparaure of microgels M-Gel2 and M-Gel4 was shifted to lower temperature. But the flocculation of microgels M-Gel5 and M-Gel6 was not detected to elevate the temperature because they contained higher content of hydrophilic monomer. The VPTT of microgels M-Gel5 and M-Gel6 was shifted to lower temperature.The load and release of drug experiment showed that PNIPAM/CS particles possessed temperature-sensitive and they exhibited good slow-released ability at high temperature. Moreover, the drug slow-released ability of CS particles and PNIPAM/CS particles in higher pH environment (pH7.4) was better than that in lower pH environment (pH3.0).