USE OF POLY(STYRENE)-BLOCK-POLY(ETHYLENEOXIDE) AS EMULSIFIER IN EMULSION POLYMERIZATION

Poly(styrene)-block-poly(ethyleneoxide), abbreviated as (PS-b-PEO) wer e used as emulsifiers in emulsion polymerization of styrene and methyl methacrylate. The block copolymers had a poly(styrene) block with M(n ) = 1000 g/mol and a poly(ethylenoxide) block with M(n) = 1000, 3000 o r 5000 g/mol, respectively. Stable dispersions were obtained when the PEO block molecular weight was higher than 1000 g/mol. Also the amphip hilic properties of the copolymers depended on the PEO chain length. B lock copolymer micelles with hydrodynamic radii between 11 and 17nm we re observed. Emulsion polymerization was performed at different block copolymer concentration at 60 and 80-degrees-C. Particle size varied b etween 50 and 300nm and decreased with increasing copolymer concentrat ion. The particle size was larger at higher temperature, but the size distribution was narrower. Polymerization of methyl methacrylate gave smaller particles when compared to styrene. The dispersions were very stable towards high electrolyte concentration, but flocculation occurr ed at elevated temperatures. Both observations indicate that the dispe rsions are sterically stabilized.