Oligo(ethylene glycol)-Based Thermoresponsive Core-Shell Microgels

Oligo(ethylene glycol)-based thermoresponsive core−shell microgels were synthesized by a two-step polymerization method: The core particles mainly consisted of poly(ethylene glycol) ethyl ether methacrylate (PEGEEMA), while the shell mainly consisted of a copolymer of PEGEEMA, poly(ethylene glycol) methyl ether methacrylate (PEGMEMA), and poly(acrylic acid). The copolymerization of the shell resulted in a higher volume phase transition temperature than that of the core. The mass of a single microgel particle was determined by both the static light scattering method and a new method using UV−visible spectroscopy. Core−shell microgels in water self-assembled into crystalline structures with iridescent colors, which were the result of Bragg diffraction. The melting kinetics of microgel crystals was studied by using UV−visible transmission spectroscopy.