Role transformation of PNIPAM microgels from stabilizer to seed in dispersion polymerization by controlling the water content in methanol-water mixture

PNIPAM-based ionic microgels with different diameters were first prepared and then used as particulate stabilizer or seed in dispersion polymerization of styrene. The role of PNIPAM-based ionic microgels could be transformed from particulate stabilizer to seed by controlling the water content in methanol-water mixture. Generally, PNIPAM-based ionic microgels served as particulate stabilizer in methanol in the absence of water, leading to the formation of spherical polystyrene nanoparticles. However, they turned into seeds when water was added into the methanol solution, with octopus-like nanoparticles obtained. Further study demonstrated that the mechanism for this role transition related to the special thermo-sensitivity of PNIPAM microgels in methanol-water mixture. They lost their thermo-sensitivity in pure methanol solution but restored their thermo-sensitivity with increasing the water content in methanol-water mixture.