pH and temperature-sensitive behaviors of poly(4-vinyl pyridine-co-N-isopropyl acrylamide) microgels

Poly (4VP-co-NIPAM) microgels were prepared from 4-vinyl pyridine (4VP) and N-isopropyl acrylamide (NIPAM) with methylene-bis-acrylamide (MBAm) as a cross-linking agent using partially quarternized poly(4-vinyl pyridine) as emulsifier, which is a special emulsion polymerization method. The morphology and hydrodynamic diameter of the microgel particles were characterized by TEM and photon correlation spectroscopy (PCS). The dependence of pH and temperature of the copolymer microgel particles were investigated and the influence of the KCl concentration in the microgel dispersion was observed. Hydrodynamic diameters of the microgel particles were drastically increased below pH 5 and those of the microgel particles were depended on temperature and KCl concentration in the microgel dispersion. The dependence of pH and temperature on the microgel particles were affected by molar ratio of 4VP/NIPAM. The cross-linked copolymer microgels composed of 4VP/NIPAM ratio of 1/9, exhibited broad shrinking transition. The swelling behavior for the microgel dispersion was much sensitive to the KCI concentration in the microgel dispersion at elevated temperature.