A facile method for preparing colored nanospheres of poly(styrene-co-acrylic acid)

• Pure & uniform colored nanospheres were prepared by heating and acid washing.
• The average particle size of nanospheres increased by 23 nm after coloration.
• The glass transition temperature of colored nanospheres decreased by 2.98 °C.

Colored nanospheres are widely used in paints, inks, food, electronic displays, textiles, and medicine. In the present study, we describe an emulsifier-free emulsion polymerization process for the synthesis of poly(styrene-co-acrylic acid) nanospheres, such that the influence of surfactants is eliminated. The obtained nanosphere dispersions were mixed with three commercial disperse dye solutions. After heat treatment, pure and brightly colored nanosphere powders were obtained by a simple purification procedure. Transmission electron microscopy images showed that the average particle size of the nanospheres increased by 23 nm after coloration, and differential scanning calorimetry revealed a decrease of 2.98 °C in the glass transition temperature. The amounts of dyes fixed within the nanospheres depended on the dye concentration of solution. The three different dyes were incorporated to varying levels, corresponding to their ability to form hydrogen bonds with the polymer nanospheres.