Abstract
New polyurethane microcapsules incorporated with an antituberculous drug, isoniazid, have been synthesized through the interfacial polycondensation of tolylene 2,4-diisocyanate with different poly(ethylene glycols) in a water-toluene emulsion. As the poly(ethylene glycol) chain is elongated, the conversion of diisocyanate decreases with time; the content of urea groups in polyurethanes increases; and the morphology of capsule walls changes, with the walls becoming looser. At high poly(ethylene glycol) concentrations, the efficiency of isoniazid encapsulation decreases owing to displacement of the drug into the organic phase. An increase in the poly(ethylene glycol) concentration above 50 vol % leads to densification of polymer capsule walls because of enhancement of the diffusive accessibility of the monomer. As a result, the release of isoniazid decelerates almost twofold.