DISPERSION POLYMERIZATION OF STYRENE IN AQUEOUS-ETHANOL MEDIA USING POLY(ETHYLENE OXIDE) MACROMONOMER AS A POLYMERIZABLE STABILIZER

The kinetics of dispersion polymerization of styrene with a small amou nt of omega-methoxy poly(ethylene oxide)(40) undecyl-alpha-methacrylat e 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 co polymer (stabilizer) after 10 h of polymerization at 65 degrees C. But as high as 98.5% conversion of styrene to polymer was attained. The i nitial rate of polymerization follows the scaling relationship, (R-p)( i) proportional to [PEO-R-MA-40](0)(0) [styrene](0)(0.92) [AIBN](0)(0. 90). It increased with increasing temperature but decreased with incre asing water content because of the solvency effect in the reaction med ium. The molecular weight M-w of polymer increased with increasing con version of styrene up to about 55%. It then decreased slightly towards higher conversions, leading to a broader molecular weight distributio n. The activation energies for the dispersion polymerization in the in itial stage (< 6% conversion) and in rate interval II were 122.3 and 6 6.7 kJ mol(-1) respectively. The characterization of the monodisperse latex particles of about 250 nm in diameter was carried out by the tra nsmission electron microscope (TEM), FTi.r., n.m.r. and X-ray photoele ctron spectroscope (XPS). The XPS result shows that the grafted PEO ma cromonomers were enriched and anchored on the surface of polystyrene l atex particles with a top surface composition of 28% macromonomer. (C) 1997 Elsevier Science Ltd.