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Different deswelling behavior of temperature-sensitive microgels of poly(N-isopropylacrylamide) crosslinked by polyethyleneglycol dimethacrylates.
Polymerization of N-isopropylacrylamide (NIPAM) with polyethyleneglycol dimethacrylates (n G, n representing the number of --CH2CH2O-- units in polyethyleneglycol dimethacrylates) through surfactant-free radical polymerization was used to prepare the temperature-sensitive microgels. The morphology, dispersity, and deswelling behavior of the microgels were investigated by means of transmission electron microscopy (TEM), ultraviolet-visible spectroscopy, differential scanning calorimetry (DSC), and dynamic light scattering (DLS) techniques. TEM micrographs revealed that it was feasible to obtain regular spherical microgels for crosslinking agents with short chain. Turbidity, DSC, and DLS analysis showed that in marked contrast to 1G and 3G crosslinked microgels, the collapse of microgels crosslinked by 9G, 14G, and 23G proceeded in a two-step mechanism. The amide groups dehydrated at the lower temperature leading to the first-step transition. In the transition, the hydrophilic long --(--CH2CH2O--)n-- segments could be enriched on the surface of the microgels, which was further verified by variable temperature 1H NMR spectroscopy. The hydrophilic long --(--CH2CH2O--)n-- segments can be dehydrated at the higher temperature.
School of Chemistry and Chemical Technology, Shanghai Jiao Tong University, Shanghai 200240, People's Republic of China., , ,
Calorimetry, Differential Scanning
Magnetic Resonance Spectroscopy
Microscopy, Electron, Transmission
Pub Type(s)Journal Article