Synthesis And Characterization Of Clay Cross-linked Poly(N-isopropy-lacrylamide) Based Microgels

The temperature-sensitive microgels based on Poly(N-isopropylacrylamide) (PNIPA) have been attracted much attention for their potential application in the fields such as drug controlled release,biomaterial separation and photonic crystal.The aim of many researches is mainly focus on the preparation of microgels with smaller hydrodynamic diameter(D_H),good monodispersity,high stability and clean surface.In this dissertation,a novel temperature-sensitive PNIPA microgel with small particle size and narrow distribution was synthesized via surfactant-free emulsion polymerization(SFEP) by u Vsing inorganic clay as a cross-linker.Then novel semi-interpenetrating polymer network(IPN) microgels and core-shell microgels with both temperature and pH sensitive properties were prepared based on the PNIPA microgels.The structure,morphology and phase transition behaviors of the microgels were studied by means of FTIR,SEM,TEM and DLS.Furthermore,the microgel particles were severed as additives to prepare the PAAc macroscopic hydrogels and PVA/ PNIPA microgel non-woven fabric.The main results are as follows:1.Adopting inorganic clay as a physical cross-linker,PNIPA/Clay microgels(NC microgels) were prepared by SFEP method.The results indicated that exfoliated clay platelets could act as effective multifunctional cross-linkers through specific clay-polymer chain interaction including hydrogen bond,ionic bond or coordinate bond.Thus the PNIPA chains were attached to clay platelets and the three-dimensional cross-linking network was formed.The D_H of the PNIPA microgel was in range from 240nm to 280nm,which was much smaller than that prepared by chemical cross-linker.The D_H of the microgels increased with increasing the clay contents,and the LCST of NC microgels still remained around 32℃. 2.The pH- and temperature-sensitive semi-IPN microgels and core-shell microgels based on Poly(acrylic acid)(PAAc) and PNIPA cross-linked by clay were synthesized by a two-step method.The semi-INP microgels were prepared in 25℃and the core-shell microgels were in 70℃.The results showed that the D_H of semi-INP microgels was about 400nm,and was not affected by AAc contents.The D_H of core-shell microgels was in a range from 160 to 240nm,and the D_H declined with increasing AAc contents.Both semi-IPN microgels and core-shell microgels can respond to both pH and temperature changes,however,the temperature sensitivity of core-shell microgels disappeared with increasing the AAc content.The hydrodynamic diameters of the semi-IPN microgel and core-shell microgels increased with increasing pH values,which was due to the contribution of the PAAc.3.The PNIPA microgel particles were severed as additives to prepare the PAAc macroscopic hydrogels and PVA/ PNIPA microgel composite nanofibers were fabricated by an electrospinning method.The results showed that the tensile strength and the toughness of the PAAc hydrogels were significantly improved by introducing the PNIPA microgel particles.The diameter of PVA/ PNIPA microgel composite nanofiber was about 200nm,which was little affected by the introducing of PNIPA microgel particles.