Abstract:

Emulsifier free emulsion polymerization of styrene in acetone water medium has been carried out using microwave irradiation. Below acetone content o f 50％, narrowly distributed nanoparticles stable in water were obtained. The average particle hydrodynamic radius is decreased from 278 to 35.4 nm with an increase in acetone content in the range 0－50 ％. When the initiator amount is kept constant, the value is increased and is proportional to the monomer concentration, in the range from 1.2 to 7.0％. When the monomer concentration is kept costant and the initiator concentration is decreased (from 0.27 to 0.027 ％ ) the value is decreased from 25 to 22 nm and then increased. On the basis that the initiator, potassium persulfate (KPS), acts as a source of surface char ge and ionic strength, both has the stabilizing and coagulating effects in the polymerization process, we have successfully found a simple formula to describe t he relationship between the particle size and mass ratio (m_monomer / m_initiator). Adding a few amount of methyl methacrylate(MMA) monomer, the size of the copolymer particles remarkably decreases from 35.4 to 16.0 nm. It has been shown that the increased stability of the resulted dispersion is due to the increase of surface hydrophilicity of latex particles. The stability and uniformity of th e final latex does not change any more before and after the vacuum distillation of the acetone from the dispersions. Consequently, we can get a high concentration latexes very conveniently by simply distill out the acetone from the latex solution.

Key words: Emulsifier-free emulsion polymerization, Styrene, Methyl methacrylate, Microwave irradiation