Synthesis of micrometer-size poly(N-isopropylacrylamide) microgel particles with homogeneous crosslinker density and diameter control

•We synthesize poly(N-isopropylacrylamide) microgels with excellent size control.•A semi-batch method allows us to control size and properties.•We discuss the role of charge stabilization on particle growth.•Homogeneous crosslinking results in superior optical properties.•We use different light scattering methods to characterize the particles.

Poly(N-isopropylacrylamide) microgel particles are synthesized using a semi-batch surfactant-free emulsion polymerization method. Particle diameter can be precisely adjusted by controlling the initial conditions, the electrolyte concentration, and the monomer feeding rate and duration. Larger particles are obtained in the presence of small amounts of co-monomer with cationic amino groups that compete against the negative charges arising from the initiator. Monodisperse particles with uniform cross-linker density, homogeneous optical properties, and pronounced thermoresponsivity are readily produced with a wide variety of diameters ranging from several hundred nanometers to a few micrometers. The charge stabilization mechanisms that control particle growth are discussed.

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