ENCAPSULATION BY INTERFACIAL POLYCONDENSATION .2. THE MEMBRANE WALL STRUCTURE AND THE RATE OF THE WALL GROWTH

The encapsulation of dibutylphthalate by interfacial polycondensation of terephthaloyldichloride (TDC) and diethylenetriamine (DETA) was studied. The growth rate of the capsule wall is determined by diffusion of DETA through the wall into the oil phase. Due to the reaction of TDC with DETA the concentration of TDC inside the capsules decreases. Both the concentration decrease of TDC and the growth of the wall thickness are linear with square root t. This verifies the model relations between the wall thickness and the TDC concentration. The rate of wall growth is a function of the polymer properties of the membrane. The concentration ratio of TDC and DETA in the oil and aqueous phase, respectively, determines the polymer properties and consequently, also the growth rate of the capsule wall. Measurements of the rate of hydrolysis of encapsulated TDC show that no hydrolysis will take place during wall formation, as hydrolysis only takes place in the aqueous phase.