Dispersion polymerization of styrene in aqueous ethanol media using poly(ethylene oxide) macromonomer as a polymerizable stabilizer

Abstract

The kinetics of dispersion polymerization of styrene with a small amount of ω-methoxy poly(ethylene oxide)40 undecyl-α-methacrylate macromonomer (PEO-R-MA-40) in the ethanol-water media was studied. A maximum and constant rate of polymerization for this system appeared at the 18% - 55% conversion of styrene to polystyrene. However, only 50% of the amphiphilic PEO macromonomer was found to be grafted in the copolymer (stabilizer) after 10 h of polymerization at 65°C. But as high as 98.5% conversion of styrene to polymer was attained. The initial rate of polymerization follows the scaling relationship, (Rp)i ∝ [PEO-R-MA-40]0 0 [styrene]0.92 0 [AIBN]0.90 0. It increased with increasing temperature but decreased with increasing water content because of the solvency effect in the reaction medium. The molecular weight Mw of polymer increased with increasing conversion of styrene up to about 55%. It then decreased slightly towards higher conversions, leading to a broader molecular weight distribution. The activation energies for the dispersion polymerization in the initial stage (< 6% conversion) and in rate interval II were 122.3 and 66.7 kJ mol-1 respectively. The characterization of the monodisperse latex particles of about 250 nm in diameter was carried out by the transmission electron microscope (TEM), FTi.r., n.m.r. and X-ray photoelectron spectroscope (XPS). The XPS result shows that the grafted PEO macromonomers were enriched and anchored on the surface of polystyrene latex particles with a top surface composition of 28% macromonomer. © 1997 Elsevier Science Ltd.