The earliest method of achieving microcapsules was the technique of coacervation. Polymers were used to disperse or suspend material to be microencapsulated. A polymer-rich phase was caused to develop in the suspension and envelop the suspended material. Further processing was required to harden the precipitated polymers to produce useful shell walls. Because coacervation was a dilute process and batch-to-batch variation was difficult to control, this technique did not gain wide practice in the microencapsulation of agricultural pesticides.
Microencapsulation by interfacial polymerization was a major step toward agricultural applications. Water-soluble monomers in the aqueous phase were reacted with oil-soluble monomers in the oil phase to produce microcapsule shell walls at the interface of suspended droplets. Although more concentrated suspensions of microcapsules could be produced by interfacial polymerization, agricultural formulations were limited to about two pounds of active ingredient per gallon. Recent break-throughs in interfacial polymerization have expanded this technology to concentrations of active ingredients typical of commercial agricultural products. Directly usable suspensions of microcapsules which can be diluted with formulating ingredients to contain four pounds of microencapsulated active ingredient per gallon have been made.