Abstract: Composition, processes, techniques, and apparatus for synthesizing monodisperse microgels based on poly(ethylene glycol) (PEG) derivative polymers by using precipitation polymerization. These microgels are hydrophilic and have the adjustable volume phase transition temperature in aqueous environment. Microgels can be added with various functional groups. These microgels in water can self-assemble into various phases, including a crystalline phase. Hydrogel films with iridescent colors were formed using these microgels as crosslinkers to connect poly(ethylene glycol) chains. The colors of these hydrogel films change with changes of environment such temperature, pH, salt concentration, etc.