A process is disclosed for performing encapsulation, en masse, by an in situ polymerization reaction to yield capsule wall material. The polymerization includes a reaction between urea and formaldehyde in an aqueous vehicle and the reaction is conducted in the presence of negatively-charged, carboxyl-substituted, linear aliphatic hydrocarbon polyelectrolyte material dissolved in the vehicle. Liquid-liquid phase separation is accomplished and maintained by increase in the molecular weight of the urea/formaldehyde reaction product without further dilution of the manufacturing vehicle. The negatively-charged polyelectrolyte material is required and has an apparent effect of controllng or modifying the polymerization reaction. The disclosed encapsulation process permits manufacture of microcapsules in concentrations of capsule to capsule manufacturing vehicle higher than previously possible.