Influence of secondary components on the synthesis of self-cross-linked N-isopropylacrylamide microgels.

This work presents systematic studies of cross-linker-free microgels formed by copolymerization of N-isopropylacrylamide (NIPAAm) and various secondary monomer components in water under standard reaction conditions. The sizes, solid densities, and volume phase transitions of these particles have been characterized through static and dynamic laser light-scattering experiments. We find that introducing a hydrophobic component, for example, styrene (St) or methyl methacrylate (MMA), leads to particles with smaller sizes and higher solid densities, while the volume phase transition shifts to lower temperatures. On the other hand, introducing a hydrophilic component such as acrylamide (AAm) or acrylic acid (AA) leads to larger particles with lower solid densities and a volume phase transition that shifts to higher temperatures and is broadened. The molar mass changes little in either case. Introducing a charged component such as sodium styrene sulfonate (NaSS) or poly(sodium styrene sulfonate) (PNaSS) leads to a sharp decrease in molar mass and particle size, and a very broad phase transition. These trends provide good guidance for synthesizing both self-cross-linked and cross-linked copolymerized microgels of different properties.