Preparation of nanoparticles by “dissolution” of submicron-sized ionized styrene-methacrylic acid copolymer particles in nonionic emulsifier solution

Styrene-methacrylic acid copolymer (P(S-MAA)) nanoparticles having high Tg were produced by a dissolution of submicron-sized P(S-MAA) particles as follows. Submicron-sized P(S-MAA) particles having various MAA contents were produced by emulsion copolymerization. Secondly, they were treated in a polyoxyethylene nonylphenylether nonionic emulsifier aqueous solution at pH 13.0 and above 90 °C. The nanoparticles having about 30 nm in diameter were only produced from the particles having MAA contents around 7 mol%, and above the contents, they were not produced. It seems to be based on that emulsifier molecules are not adsorbed onto the polymer molecules enough to dissolve them. The effect of MAA content on such a dissolution behavior was examined using seven kinds of different nonionic emulsifiers having hydrophile-lipophile-balance values between 12.2 and 18.2 at various temperatures and initial pH.