Process for the polymerization of shear-stable water-in-oil emulsions

A process for producing water-in-oil emulsions of a polymer from at least one ethylenically-unsaturated monomer comprising the steps of

• (a) forming an aqueous phase comprising an aqueous solution containing at least one ethylenically-unsaturated, water-soluble monomer;
• (b) forming an oil phase comprising a hydrophobic liquid and an oil-soluble surfactant;
• (c) blending said aqueous phase and oil phase to form a water-in-oil emulsion of said monomer;
• (d) initiating polymerization of said monomer in said emulsion by heating said emulsion in the presence of a first polymerization initiator capable of initiating polymerization of said monomer at a temperature less than about 45.degree. C.;
• (e) after a small amount of polymer is initially formed sufficient to provide a shear-stable monomer emulsion, completing said polymerization in the presence of a second polymerization initiator capable of initiating polymerization of said monomer at a second temperature which is both higher than about 40.degree. C. and higher than said first temperature;
• and
• (f) cooling said emulsion during said polymerization by continuously withdrawing at least a portion of said emulsion during said polymerization, circulating the withdrawn portion through an external heat exchanger and returning it to the reaction medium.