Agglomeration of latices by organic acid--anhydride mixtures

A process for preparing rubber modified graft copolymers by grafting large diene rubber particles with alkenyl aromatic and alkenyl nitrile monomers comprising:

• A) forming an aqueous latex containing water and diene rubber solids, said rubber being dispersed in said latex by a surfactant as particles having a weight average particle size diameter of about 0.05 to 0.20 microns;
• B) adding a water soluble organic acid and a water soluble organic anhydride to said aqueous latex;
• C) agglomerating said rubber particles contained in said latex to larger agglomerated particles having a weight average particle size of between 0.30 to 1.0 microns, said larger agglomerated particles comprising less than 2 percent by weight coagulum having a weight average diameter of greater than 0.42 microns;
• D) stabilizing said larger agglomerated rubber particles in said latex by the addition to said latex of a sufficient amount of an ingredient selected from surfactants and bases;
• E) polymerizing a mixture of alkenyl aromatic and alkenyl nitrile monomers in the presence of said stabilized latex to graft said agglomerated rubber particles with at least a portion of said monomers and to form an ungrafted alkenyl aromatic alkenyl nitrile matrix polymer, thereby forming a latex containing said grafted rubber particles and said matrix polymer;
• and
• F) separating said matrix polymers having said grafted diene rubber particle from said water.