Abstract: An emulsion polymerization process comprises subjecting an intimate aqueous dispersion of monomer material comprising at least one vinyl aromatic monomer, optionally with unsaturated nitrile or conjugated diene comonomer to a rapid polymerization, preferably adiabatic, in the presence of a particular emulsifier system in a continuous flow agitated reaction carried out at 80.degree. C. to 100.degree. C. The thermoplastic product in latex form is continuously removed and is ideal for use in reinforcing rubber latices. An advantage is that a small reactor may be used to obtain a large throughput.