Manufacture of polymeric materials

Aqueous dispersions of polyvinyl acetate are obtained by emulsion polymerization in the presence of polyvinyl acetate hydrolysed from 78 to 92 per cent, a persulphate catalyst and an alkali such as sodium carbonate or hydroxide. Ammonium, sodium and potassium persulphates are the specified catalysts. Neutral salts, such as sodium chloride, may be included. In examples the vinyl acetate and the catalyst are added continuously at rates that maintain a constant monomer/catalyst ratio. The stepwise addition of catalyst is also illustrated. The particle size of the dispersed phase may be from 2 to 6 microns.