SOLUBILITY PARAMETER EFFECTS ON MICROENCAPSULATION IN THE PRESENCE OF POLYISOBUTYLENE

A nonsolvent/solvent evaporation method of microencapsulation using ethylcellulose and ion-exchange resin-drug complex was used to show that solubility parameters of the microencapsulation system affect the ability of polyisobutylene (PIB) to promote mononucleated microcapsules. Microencapsulations using solvent systems which had solubility parameters well within the PIB soluble region of a two-dimensional solubility parameter map produced nonaggregated microcapsules which exhibited similar morphological characteristics. Whereas multinucleated microcapsules were produced when solvent systems were used which had solubility parameters close to the region of insolubility for PIB. Further examination of solubility parameter maps of ethylcellulose as affected by polyisobutylene demonstrated that PIB altered the phase changes of ethylcellulose. The formation of two liquid phases induced by polyisobutylene can be used to explain how mononucleated microcapsules are produced using the adjunct polymer PIB. The use of a solubility parameter map for the coating polymer ethylcellulose, as affected by the adjunct polymer, polyisobutylene, can be used to choose solvent systems providing related phase changes and consequently similar microcapsule coats.